Technical 1948 oldsmobile rearend

I have installed 350 rocket engine and 350 transmission what would be the best route to go for the rearend . The one in car is trashed

 

How trashed is "trashed"? They have a removable center section, were the same through 1956, and had several gear ratios available.

 

My '47 Buick has a mid 70s Monte Carlo rear & it fits well.

 

i second the motion on chevy rear ends...

 

Where would I get parts for original axle . Chevy axle would that be like a 10 bolt

 

Parts?
Well the Googler will tell you that most rear end stuff from a 39-56 Pontiac or Olds will fit.
A '57 Pontiac rear will be expensive but a '57-59ish Olds rear would last forever too.