906 vs 452 heads on 440

Here are some intake airflows from our flowbench. These are generalities and flow from different ports on the same head will be different. Also sometimes the 452 will flow a little better than the 906 and sometimes the other way around as in this case.

Lift..........906.........452

.100.......66 cfm...61 cfm
.200........130.........130
.300........189.........188
.400........222.........213
.500........234.........227
.600........237.........230

Do a valve job only on the heads and you would probably not be able to tell the difference in the power they would make.