I believe they are the same part, the last number probably has to do with the casting date.

See http://www.ply33.com/Models/P4/#specifications

6.7:1 was standard but they also offered a 5.2:1 compression ratio "econonmy" version. I'm guessing that was for using very low octane unleaded gas.

Don't know the difference in casting numbers on the head...

What is the stock compression ratio of the P4 engine?

My cylinder head is marked 632955-1. What is the difference between this head and 632955-3?

As always, Thanks in advance!