Man, with as much trouble as I'm having with a simple carb swap, I'm definitely thinking slapping a turbo on top of it is just asking for trouble. I should've taken the time to label all those frickin' hoses somehow, but decided to take lots of digital pics, in the hope that those would be better.

I've looked at the pics again, this time on my laptop screen, and will check the routing of the hoses again tomorrow. If I'm certain that the hoses are correct, and it still won't idle below 3000 rpms, then by process of elimination I'm going to assume there's something mechanically wrong with the replacement carb, and send it back. I don't have the patience to screw around with this thing, so if checking and rechecking the hose connections doesn't fix it, the carb's going back...