Those engines are about 700's, correct? With 1.5 ratio drives, I'd think you'd want around a 27p. There are some 28's in the classifieds that might work well...
Franks Cafe ran about 78 with 550 a side and bravos. It was running 76 before Brett labbed his 26 Bravo 1 props. I thinks the right props in Mikes case here will make a night and day difference.