Easiest I can think of would be a 3 pot manifold with 3 TBI units off say a 2.8 GM (depending on what size your 6 is) with a Megasquirt control.
I expect that would be simpler than trying to get even distribution with port injectors.
It should still allow a batch fire, and IIRC they have 2 injectors each so that is still 6 injectors, most aftermarket controllers should be able to handle that.
Megasquirt you build yourself, so you build what you need.
