You used an Edelbrock carb both on the dyno and on the street? IMO those tend not to like huge plenum volume because they are signal sensitive. That shows less on the dyno than in part-throttle loading on the street. Holleys are the same, but seem to be more easily band-aided.

I bet that Wilson 2-inch tepered combo spacer really worked on the RPM. I usually find them to add some top end without hurting power anywhere. Then sometimes they don't work at all. Carb spacers are voodoo.