I have a 77 Aspen wagon that came with a 318 auto and a 3.2 something geared 8.25 rear. I have a warmed over 360 that is somewhere between 350 and 370 hp. My questions is will the 8.25 handle the power and live?

How good is your traction. Auto or stick.i have seen them holdup behind bb Dakota's but they have beefier axles.

A LOT depends on how you drive it, and the grip of your tires. If you don’t use heavy throttle in turns, and limit burn offs it will likely do just fine. That assumes it’s in good shape to start with of course.

Auto`s seem to hold up fine with a 8 1/4. I raced back in the day and had no issue other than the stock sure grip giving up. Now the 904 was a different story. For added insurnace I have this new rear cover that I never installed. https://www.jegs.com/i/LPW/619/301-10C/10002/-1

It'll more than likely be fine. If it breaks? A B body 8 3/4 is a bolt in using a factory 727 Duster drive shaft. the 81/4 brake parts will bolt up as well.
Doug

Not really, at least not without new axle shafts. bolt pattern and flange offsets are different.

Ran an 8 1/4 behind a warm 360 and an A833 in my Diplomat for years. SG with P255/60R15 BFG's. No issues

I broke one once. it was out of a 73 Duster 340 car with near 100,000 miles on it, installed in a 35 Dodge 2 door sedan with my 150lbs son sitting directly above the rear end. It was a "limited slip" 3:55 gear rear.

It was a fairly cool Sunday morning, we were heading to a car show. I was having issues with the carb. The stupid thing would cough and die every time I was trying to get through a stop sign on a busy street. After about the 4th attempt, I put the car in neutral, revved it to about 2500, and shifted it it into drive. Away it went, for about 2 feet before the bang and the sound of breaking gear teeth joined with the car no longer moving under power. Lets say we didn't make it to the car show that day.

One of the two bolts that holds the carrier bearing cap on one side broke off even with the housing and allowed the carrier to get cocked. That action stripped off about 6 teeth from the ring gear, and most of the teeth from the pinion gear. I replaced the 8 1/4 with a 9 1/4 I had in my pile of parts.

The odds are about even that if my son wasn't sitting directly above the rear end, the tires would have spun and the rear probably would have survived. It is also possible that the failed bolt was already cracked from previous abuse. I bought the Dusted used, and beat the crap out of it, then I beat the crap out of the sedan before the axle failure. The axle failure didn't change my driving habits, I was pretty used to accumulating broken parts.

How tough that 8 1/4 is depends on how bad you plan on treating it. My broken 8 1/4 went 100,000 miles on the street (and the strip at least a few times) before it got to me and then was in the sedan at least 3 years before I broke it with the neutral drop.

I run a 8 1/4 with 3:73 sure grip behind a 470" stroker 4 spd in a 69 Bcuda. I'll guess it north of 525 hp. It's been in there for years...zero issues. I don't put sticky tires on it and I don't do 5k rpm clutch dumps. With 255 BFGs they lose long before the diff does....the tires are the fuse. If they spin the diff will live a long life.

Hmmm, the drums off my 73 8-1/4 are the same as the 68 b-body 8-3/4, same for the shoes and backing plates.

Ah fudge, I read it as an A body 8 3/4, not a B body one, you are correct there.

I'm not sure what tires I'll run on it. I'd like to use the factory wheels so I'll more than likely stick with 235/60/15s. I want it as a parts chaser and will horse it from time to time. It probably will never see the track. I do have a fresh 727 auto that I will use. Not sure if there is a factory driveshaft for this set up. This is a project that my best friend bought years ago. It sat in his barn for close to 20 years. Last year I built the 360 for him. He passed away a month ago and I got the car. I want to build it the way he wanted it. The shop that did the machine work squared and decked the block. We set it up with good quench, 9.8 to 1 compression. A set of 915 heads, gasket matched and light bowl work. A 72 340 intake for now. I can't find the cam card but the guy I spoke to at Comp Cams said in a 9.0 to 1 and otherwise stock 360, it made 363 hp.

I think you are thinking of A body with 1 3/4" shoes. The bolt pattern of a F body and a B body are the same. The 66-70 B body axle is 3/4" wider overall. So 3/8" on each side. The driveshaft definitely works. So do the backing plates. Both are on my Volare currently. I have heard some 8 1/4 backing plate are missing the lower hole which can be drillled.
Doug

I've had several factory 8.25 rears in AHB Diplomats that I've put in a warmed up/heated up engine. Mine have always held up well. I put 60k miles on my first one with a MP 360/300hp that was pushing 400 lb/ft torque. And this is after the car was used as a police car so the rear end had plenty of miles on it. I had 2.92 and then 3.21 gears and 235/70/15 on factory rims. My current one has a stroked 408 that dyno'd on engine stand at 469hp and 528 lb/ft torque and it's held up perfectly. Same tires and a 3.21 rear gear and sure grip. I don't beat my cars but I certainly enjoy a good punching it now and then and a little tire smoke occasionally. As written, if you aren't running fat slicks and making a bunch of hard launches you'll be fine. I think the 8.25 is underrated.

Also if you find one out of a police car it will have the setup for the larger 11" brakes.

The 904 will fail before the 8 1/4 will.
For the driveshaft one from an M body will fit and there are ones out there with 8.25 and 727 but it would be easier to get one shortened. And of course the yoke is different.

for what it's worth if you're looking for deeper gears on the cheap, a jeep XJ cherokee after '87 uses either a dana 35 or an 8 1/4 in the rear. the easiest to find are 3.55 geared 8 1/4's that typically came in autos. manuals had 3.07's, I think the tow package had 3.73's...they are 60.5" wide, basically the same as an FMJ, and I can find them all day on facebook marketplace locally for $150 or less. just need to cut off the shock mounts and spring perches, and weld new spring perches in the correct location. IIRC the spacing is about right, but they're on the wrong side of the axle (spring over vs. under)

also, the rear disc brakes from a liberty or late 90's grand cherokee with an 8 1/4 are a bolt on if you want rear disk.

97 and up are a little stronger

I have a 69 Dart stroked Magnum small block 11.50 in quarter mile. I have a 8 1/4 rear with 4:10 gears. Hoosier slicks. 727 auto, 4k stall. Launch with no slippage. Car launches hard. The only mod other than gear ratio. Is an aluminum carrier bearing braced dif cover. Hundreds of drag strip launches. Rearend is fine. I have zero worries about abusing the rearend. But I do have a narrowed 8 3/4 ready if needed.