GM engine ID.

GM engine ID.
Hello, everyone I'm looking for some help identifying a GM engine which my son purchased at a swap meet. OK what I do know: block casting NO#10243880 = 350ci 95-00 block
1 M 01 26 = chevy-Mexico- January-26th.

What I don't know is the following (and a lot more but we won't get into that right now ok) The code- 4R34 is on the front right hand side of the motor, what does it stand for? Any help would be appreciated.
Thanks alot Rick:

  Rickss396