I worked on one of those a long time ago. We pulled it off , just too many issues to make it work.
The reason the injector holes were welded up in yours is because in its stock form , it had these screw in injector bungs that leaked vaccum like a sieve. We thought about welding ours back then too , but sold the thing unmodified.
Im sure that the rail and other hardware was not an original rail and aftermarket to finish the modification started on the manifold. I remember seing the ad for sale on your manifold.