I am trying to swap a small block motor to a big block and was wondering if anyone could tell me what the dimension from the motor mount on the 350 motor to the mounting surface of the transmission? And is it the same as the motor mount position on the 455 motor? I am also wondering if I will have firewall issues?

 

Welcome. I moved your post to it's own thread. This topic has been covered many, many times. Start by reading this thread.

The only external difference between a 350 and 455 Olds is the deck height. This is a bolt-in swap. Use the 350 motor and frame mounts.