Man, I love those old Chevy II's!! I agree with 75GMCK.. The most cost effective package would be a turbo 350 tranny behind a 350.
I am going with a THM 350 in my Chevelle in place of the powerglide. It has the same 1st gear ratio as a muncie. They would be better around town for MPG than a powerglide and much easier to do a burnout with.
Im building a 327 from a 350 core to go in my 65. I highly reccomend David Vizzards books. You can make up the cost easily.
I strongly disagree with the statement that a 383 costs the same as a 350. Not too many scat cranks in junkyards. Lots of machine work inherint in a 383 project and a 350 can be reworked pretty cheap. 383's are nice, but not cheap.. If I wanted a motor for pure power I would just find a good 2 bolt main 400 and go from there.
From a cost standpoint though the 350 is by far the best..
Oh! and a THM 350 will bolt right up in place of the powerglide. You just need to fiddle with the linkage to get it to work. I think I will go with a floor shifter.