keithdoxey, If the PCB has some complexity to it and you have many already made why not think about a small transition pcb that has a pin header to plug into the exsisting PCB processor socket, and a socket for the new processor? I have done this in the past for upgrades of old PCB rev's during the transition to new artwork. The small pcb wouldn't be much bigger than the exsisting processor.

Dave Purola,
N8NTA