I know exactly what you mean, i'm was trying to get some info on my 66 toronado 425 motor but i cant find hardly anything about them. But if your looking to REBUILD the motor yourself just buy a engine rebuilt kit, i saw a COMPLETE rebuilders kit (rings, bolts, valves,oil ...etc) on ebay, just search for : oldsmobile 425 engine kit and on the bottom there should be a basic and a deluxe kit.
I personally don't think you should rebuild it but instead get a remanufactured engine. When rebuilding you got to send the motor several times to a shop to get it bored and all that stuff, and they wont warranty their labor. On the other hand the remanufactured motor will not only cost you less time, but money in the long run and they usually have a warranty on it (they will even paint the motor anyway you like just send them the paint
)
I hope i was a bit helpful
