Although I've got a couple of crash box 4 speeds stashed away, I'm no expert concerning the differences in them. I'm reasonably sure the Chevy engine will also bolt up to that bellhousing, which has a different transmission bolt pattern than the 48-up synchronized boxes. Definitely follow the leads the other guys have given you. I've got one GMC engine on hand, a 228, but I'm in middle Tennessee- - - -probably more of a road trip than you'd want to make!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!