Hi. Does anyobody have an idea of how many hours it would take to install a 440 rear main seal on a 1970 B-body? Thanks.

Ten times longer the first time than the tenth time
AKA, the first time doing any thing automotive for a novice is always harder.
All the Mopar cars made since 1962 up to 1974 need to have the center steering link between the pitman arm and the idler arm removed to get the oil pan off, you will probably need to loosen up all the main caps to remove the upper seal also
I would plan on 3 to 5 hours start to finish, maybe longer on the first time if you have all the tools you need

there has been some excellent threads on the caveats regarding this pesky situation (repeated leaks). See if you can retrieve em (I ain't up on it but see if you can) or someone might post a link to one or more of em. Good info was posted.

Up on a lift wouldn't be bad. Flat on your back in the dirt is a little different. You can get it done either way, though. 3 to 5 hours is just about right.

Make sure you have all the required parts and gaskets before hand don't assume you can go to the parts house and they will have them on hand.

Either way, allow time for a shower afterwards. Wear glasses or goggles and keep your mouth shut while under the engine. Dirty oil in your eye or mouth is no fun.

No matter how many times you have seen the nitro guys tear down a hot bottom end do not attempt this with a hot engine.

MOST importantly - DO NOT I repeat DO NOT let your wife catch you putting your oil soaked shirt in her new washer. Don't ask me how I know this.

Wear one of these.

https://www.harborfreight.com/face-shield-with-flip-up-visor-62995.html

SUPER CHEAP way to keep junk out of your eyes and mouth, while also keeping said junk off your face. even if you toss it after the job is done.
pick one of these up before you start !

I normally will let the car set over night or longer after draining the hot oil out of the motor before working on the opened bottom end
I have had to remove more than one oil pan in the driveway on my back in the winter at night after work, no more
Enclose shop now with a cement floor, nice creeper and heat

Rope seal or rubber seal?