would a distributor work with that casting or would they have needed an offst?

Possibly the reasons you don't see more of them are:
1) distributor issue
2) looks to weigh as much as an iron oem manifold
3) runners look to be too long

for comparison, look at the runner length of this tunnelport version:



The TP version looks to be lighter in weight and the runners are noticeably shorter (and clearance is provided for a distributor). Runner length tuning would have been via the ram tubes with maybe an airbox mounted to the ends of them.

Someone was experimenting, doesn't mean the experiment panned out, other than in producing a rare item.

You're looking for an art collector, someone to put it on a pedestal. Good luck.