Yeah the later revision. But you would need to know the logic board revision from the Seller as outwardly they all look the same. The 9500 is 100% supported, as is any other box with the same revision logic board (7300, 8500, etc.) in to which you could put a dual processor CPU card.
I was a powerpc hold out and used them well in to the mid 2000’s. it got used less and less. I only put my 9500 in storage when I moved about 2 years ago. I’ll dig it out at some point. The Dano build is worth finding. I have a video of it on YouTube that I linked to earlier (I don’t post much you’ll find it if you look at my posting history)
Your bebox will probably never boot past the DR’s. the boot ROM is too small. Without the original boot ROM source code, you have no chance of making PR or later booting. Maybe someone could ask ACCESS to release the bebox boot ROM source. It was a separate self contained bit of code, as was the boot ROM app and the Mac version of the boot code (Mac version compiles using CodeWarrior.)
But honestly, between a 604e and 603 processor based multiprocessor machine, the former is much faster and better experience. You could also look out for one of those quad core Mac clone beats. I always wanted one of those.