I have a 50 fastback with the straight 8 and standard transmission. It is driveable but I need to do a good bit to it. I envy that front grille! Mine is pretty much toast! I wonder if there is any way to hook up a more modern (60s-70s) 4 speed to the straight 8?
Have you checked the Pontiac Chieftain group on Facebook? If not, here is a link:
https://www.facebook.com/groups/150467135123404/