I put a 350 in my '84 NA a few years ago,and it was a pretty easy swap. Of course the ease of the swap depends on your experience level. I fabbed my own motor mounts and rear cross member, and used a TH350 tranny. Going with a manual would be a bit more complicated, but not a lot. As for being able to clear a blower, I wouldn't count on it unless you dry sump the engine, or use a pro charger. Of course a Z31 looks really good with a cowl induction hood.
Good luck on the build,
Joe