The divider has a notch cut out to connect the 2 sides. I tried a 4 hole spacer and an open spacer back to back on the dyno.

Not surprisingly, the 4 hole had more under 4,500rpm (10+/-) while the open had more over 4,500rpm (20+/-).

I ended up with a 1/2" wood open spacer. It really dropped the carb temp, too.