Im building a 355 Vortec motor for my truck thats TBI Equipped, Im using a Edelbrock Performer EPS Intake, I picked up a 1" spacer the other day with an interchangable inner core between "open" or 4 hole, Well I took the 4 hole and modded it out basically making it a split just like most of the square bore intakes, basicallly the plenum remains the same but 1" taller, you think I should use my custom plate or the open plate? Which would make more power? of course the TBI adapter plate will sit on top.

 

If it were me I would use the open spacer, for one reason. The engine's firing order doesn't evenly alternate from bank to bank. However your injector pulses do. I would think that the open spacer would allow a slightly more even mixture to each cylinder at WOT. Try is both ways and dyno it.