FWIW, and few will remember, the outlier one had to be aware of. That's the '68-'69 RR 383 with the + deck. I couldn't put 915s with steel shim gaskets on my '68 way back so I had a valve job done on the 906s.
Not sure what problem you had, but the only 383 block that was a tall deck was in 1959 or so. 915s go just fine on any 383 block given the correct intake.
