Been there and done that in a 1987 IROC. I did not have that heater box in my car prior to doing it, don't think it would have fit with it. It's a very tight squeeze in that engine bay!
Friendly tips... stock fans fit. No need to smash the firewall to clear the distributor (I read that EVERYWHERE back when I did it, it's just your typical "he said/I'll repeat" internet lies from people who have never done it). Manifolds won't clear frame rails, they have a set of headers off a G-Body (I believe) that fit if you beat the passenger side floor pan up a bit + grind that side's motor mount down a hair and they only cost like $180 (Part #8012 if my memory serves correctly). I spent days trying to get the manifolds in there... a set of long tube truck headers did fit but the clearance from the ground was about 1/2" lol.
Best way to install the motor is the same way as any 3rd gen motor installation. Take one motor mount off the block side (usually passenger side is what I do). Lower the motor in place, mate it to the transmission's alignment dowels, toss a few bellhousing bolts in loosely to keep it from separating, install driver's side motor mount bolt. Rechain the motor from the passenger side head (exhaust bolt holes). Lift the motor up so only the passenger side raises. Quickly grow a set of balls and install the motor mount back onto the block (then realize how stupid of an idea that was) and finally bolt it in place. Tighten bellhousing bolts and continue installation. If you think it's a joke, check out the last picture. You can see the motor mount on top of the overflow tank.
Did it so many times I could have a motor back in a 3rd gen in a few hours.
Go for it. I did it a few years back when I was 18 in the middle of winter (outside lol). My 454 had ported/deburred peanut ports, a mild cam, flat tops and was punched .060". I never got to drive it with the big block in it, piston skirt whacked one of the walls and busted a skirt during break in.
Too bad you don't live closer. If you fed me and supplied the beer I'd give you a hand.
