800cfm spread bore thermoquad compatibility?

Yes. Unless you put down the gasket and there is enough meat of the intake carb mounting pad to carve up with the die grinder to take that route.... if you wish to do so.
But I don’t think so.

I know you just scored the carb but I figured I say you’ll be better off and much more happy with the large primary TQ. Been there done that on a B 400.