How hard is it to change main and rod bearings while
the engine is still in the car.
Any suggestion on how to do it? What to look out for.
I will be installing a new rear main seal as well.
71 Dodge Challenger
440 based 512 ci Automatic Trans
8 quart pan. I have the pan already out without moving
the engine from its mounts.

Also,
I just rebuilt my 727. I am pretty sure that I adjusted the rear band.
My question is.
How can I tell if the band is adjusted without removing the pan?

Old age has me second guessing if I adjusted it.
If I did, I know that it would be done correctly.

So, is there a way to tell? Maybe by just turning the drive shaft?

It's easy to change the bearings in the car. You just need to rotate the old mains out and the new ones in. Rotate the crank toward the tabs to come out and away to go in with the new while using a plastic strip to push on the bearing if necessary to get it to come out.. Rod bearings are no trouble at all.

One thing he'll be saving is alot of parts money. Oh, and a bunch less work. I've done that change in my driveway in about 3hrs including time to drop the pan.

Before I took the tranny out I did a leak down test and all of the cylinders where fine.
I had a crack in the bottom of my oil pan that dripped a spot of oil when the car sat overnight.
I cleaned the crack up and ran silicon on the crack as
a band-aid. I now had the time and with the car on my buddies lift for the tranny job. I decided to fix the pan. While we were in there I thought might as well check the mains and rods. Rod bearings look good. But for 100 bucks why not install new. I beat on the engine allot.
After inspecting the mains I see some slight galding. I think its from over gassing the engine. Meaning running it to fat. ( now fixed, changed jets) The trust bearing had a clearance of 8 thou. and worn to the copper.
Removed another main and it looks pretty good. Normal wear.
so 100 bucks more. It's more of an insurance policy for another
couple of years.

This engine has about 100 passes at the track and couldn't even tell you how may HARD street miles are on it. I have been running the 512 for almost 4 years. Keep the oil changed and a wix filter. Just thinking that now is the time.

Thank you for your help.

You need to pull the pan to check the rear band. Did you change it? Did you loosen the adjuster when you built the trans? If not, it is probably fine, otherwise, you should check it.