I can understand your desire to upgrade your carbs, those probably could
use at least a rebuild. Assuming they are originally the correct ones for
the engines, just getting them rebuilt would likely solve any problems you are experiencing.
Many newer carbs could be adapted to those engines but it would be up to
you to tune them to match what you have. Big block GM/Chevy engines will
always have parts and services available. Carb rebuild shops are out there, I'd check online.
Science doesn't care what you believe. -Neil deGrasse Tyson