I have an old '79 Chev with a 400SB in it. Great motor. I think you could TBI it if you had the skills. Same motor basically except some modifications to it as well. Idk if you take the TBI injection setup and put it on a 400 and tune it I'm sure you could get it to work.
I'd say you'd need a bigger TB and injectors to harness all the power of a beastly 400 though