You need some taller back tires

Years ago I drove my 71 Challenger to Carlisle with 4:30 gears

At the time it had the Blower on it , stopped every 100 miles to fill it up

was with a group of friends and they thought they would blast past me coming down RT 81 , they figured I couldn't or wouldn't keep up

The looks on their faces when I did pass them at about 100 mph with the blower screaming and the engine wound up

Ditto on the taller tires. Back in the days, my 70 Challenger was running a 4.10 dana w/auto. Was my daily drive for two years, travelling every weekend from MD to VA on I-95; wasn't too bad. Had L70s x 15 tires in rear (yes, L70s for those old enough to remember; Hijackers were maxed out at 150 psi to prevent occasional fender rubs). The other 70 had a 4.56 dana (4-sp w/L60s x 15) which was almost unbearable to drive, again on I-95. Had to leave around 1:00am to prevent any traffic tie-ups and truckers from running me over in the slow lane. Drove the minimum 45 mph speed limit the majority of the time, on occasion up to 55. Took about ~4-5 vice ~2.5 hrs for the other Challenger. As someone previously mentioned, stop-light-to-stop light was the fun part with the 4.56's.

i ran 5.38 gears in my charger for a while.
they were fun, but that eventually wore off and i swapped to 3.91's.
the car was as fast with those, and had more mph at the stripe to boot. imagine that.

I run 4.56 gears on a 29” tire. Needless to say, I don’t leave town.

If you use the right parts a 727 based trans will be fine at 1000HP, look at the Cummins powered rams making more HP than that , and the torque is even more than a gas engine . If you build the OD unit to Diesel specs you should be fine, the issue you may have is getting a lockup performance convertor for a gas engine in the stall you want? But they are making them for turbo 400 racers so there must be something available ?

Its not 1980 any more.... set your rods and mains at .003, deep pan and good oil, optimized cooling system and hammer down. The most friendly gear I drive is a 4:30 the better is 4:56 and its happy in the 5-8k area. Nothing better then running 65mph and someone thinks your spent till you pull it down one and then they know the real truth.

I think back in the day the mostly stock bottom enders would of benefited from a bit more bearing clearance and better rod bolts.

Some have got complacent just cruising and cant/wont even run off a stop light which for some isnt a bad thing considering stock or just above stock cant muster a win over some modern V6s.

In the 80-90-s old iron still ruled over anything new.... no longer true.

My black one has 3.54s and is fine on the hiway even at 75 mph , but it is up there for RPMs . Its a hemi auto

My yellow has 3.91s and is a LOT more fun around town . but is screaming at me at anything over 65-70 mph its a 383 auto

Both have a 27inch tall tire

I have run 4.10 for yrs (30) in a 416 sm blk been 20 miles to 2000 miles & just under 2700 RPM but i run a 32 tall tire, keeps it at the 2700 RPM . Just like to get out on the interstate or old country roads people don.t expect to see our old cars there. To me it,s all about the smiles per mile

I was talking w/ a mechanic,and was told it's a real PITA to put a new ring and pinion in a Dana. Looks like I'm sticking w/ the 4.10s

I would guess he didn't have the tools needed. Ive done it on stands but a lift would make life easy.

Same here. It's not too bad with the correct tools. I have the T&D installation tool kit. It includes all the extensions and pieces for all the popular rear ends. I put 4:10's in my Dana in my Challenger.

Find a new mechanic.

Most vehicles have integral rear gears. If the 'mechanic' said the Dana 60 is hard to set-up then he must not be much of a differential guy.

look for a "rear end" guy.................[i couldn't resist. ]

Just for the record your honor, I said A mechanic, not MY mechanic! lol

Yep this is the way to go really. Convert the trans. As much as I love the bullet proof 727, if you really wanna have the best of both worlds....

Swapped in a 518 and could never EVER go back to a 727.
3:73 gears, only 2500 RPM at 80

Agreed , the guy either has never done one or just doesn't want to make money unless it's a job he can charge book time for that he can do for less. I bought a case spreader just so I can do them myself .

Mark swap a ford 9" in and I bet the guys answer will change ...

So is a ten bolt and twelve bolt GM rear end, any non drop out rear end has to have the gears set up in the rear end housing, I bought the tools, bearing puller and pinion depth tools to do my own. I take the housing out of the car and set the new gears up in the shop so I can keep it clean, warm or cool and take my time doing it correctly. I did make some set up bearings also, which helps a bunch on setting the rear ends up