After I blew up my 307, I had a Chevy 350 in my 442 for a couple years before I built my 455.
The 350 swap was a huge learning process for me, as I was only 18 and had never taken on something like that by myself. Now that I know more, it's truely very simple to do, and I had my wagon swapped over from a 3.8 to a SBC in about 5 hours.
The 350 I had was in my running and driving '85 Blazer, so it was nice and complete. I drove the truck into the shop at 5pm, yanked the motor, and pushed it back outside at 6:30pm. I replaced valve cover gaskets and that's it. Cleaned it off, painted it, and dropped it in after I swapped out the motor mounts in the 442.
I didn't even move my battery or vapor canister, I just lengthened the wires to the alternator. I also had to lengthen a couple wires for the starter.
I ran my original carb, still hooked up to the computer, and got an electronic distributor that worked with the computer as well.
The 200-4R didn't need to be changed out, so I got lucky there.
Swapped the motor mounts, got some new radiator hoses, an alternator bracket, and that's about it...
Oh yeah, and I had to slightly shorten the rubber fuel line to the pump so that it didn't curve so much and pinch itself off.
I had already removed all the A/C stuff from the 307, so that wasn't an issue.
I also had to modify my exhaust so my new SBC headers would mate to the pipes I had for the headers for the SBO.
One thing I didn't do was to get the proper brackets to hook up the P/S. I just had the pump tied up against the frame rail. That's the only thing I would've done differently. It was hard to turn, but I got pretty strong in my upper body pretty quick, since I drove the car as much as I could back then, since it still got 17 mpg.
It's really not that hard of a swap.