Really it wasn't any worse than a regular engine swap when I did mine. However, I went the easy route and did a carb swap (no ECU or wiring with my engine when I bought it) originally and just bought an MSD box for the spark. The swap mounts and flywheel/flexplate make things pretty much bolt in. You have to give up a few things (like power steering) and have things pretty ready to go, but all in all I did essentially zero modifications from stock components during the initial install. Not saying you don't to have and hunt down the right stock pieces, but no real fab work was required. I dropped the engine right into the bay one afternoon and had the trans bolted up a few days later when my clutch showed up. However, there was definitely some tinkering with sorting out some of the wiring (mainly a switch 12v source under the hood) and trying to do things the "right" way as opposed to the short way. The prep work was really more what it was about than the actual swap. Test fittings parts on the engine out of the car while I had room to work was one of the better choices I made.
However, as Aj408 pointed out, the more I got into things the more I had to fix in general. I've since ended up swapping back to fuel injection (got a deal on a computer), swapped over to a 6 speed, and cleaned up a lot of the little stuff while I had the extra room. Latest plan is to clean up some of my wiring to make things a little more presentable and accessable.