The difference is in the heads.
MPFI heads are the same as the carb heads in everyway EXCEPT in the bolting pattern of the intake manifold. This is because the carb intake is one large hole and the MPFI intake has two individual ports per head.
There's small differences in the back of the block but these are easily delt with.
So basically without removing and swapping heads, it's a no go unless you mod a carb onto the MPFI intake, but this could also turn out not to be ideal since the MPFI intake is not designed for an air fuel mixture. This may turnout to not be an issue if you're willing to take a punt.
Cheers
Bennie