I am in the process of fixing some minor problems on my engine, so I have it out of the car and has taken off the oil pan. I found the engine very clean inside, and it appears to have been rebored and the crank seems to have been reground. I found som text written on the crank:
RR
R10
M10

I guess R10 means rod bearings are reground .010" and M10 must mean that the mains are reground .010", but what can RR mean? Is it the engine rebuilders signature? Could it be an abbreviation for something?

I'm trying to think of what it can mean, but since english isn't my first language, I'm turning to this forum hoping that somebody can help me guess.

RR is probably the Shops initials, Is that a 455 or 428?

I suppose you are right about it being initials.

The engine is a 400. The block comes from a 1970 GTO but most of the other stuff is 1969 (like my car).

I noticed that it's drilled for 4-bolt mains which should make it a RAM AIR 3 block.

You are right about what the R and M are for. The crank has been turned 010/010. No problem with that. When you get pass 030 then you have problems.

I'm fairly new to Pontiacs, so I could be wrong, but I think the same blocks were used for R/A and non R/A engines, at least in 1970, where this block originates from. Different bearing caps (2- or 4-bolt) were obviously used.

My block has casting number 9799914 and YS as the engine code. That translates to a 1970 350hp GTO without Ram Air according to these pages:
http://www.pontiacpower.net/engcast01.html
http://www.pontiacpower.net/engcode01.html

You might be right, most 400 blocks are drill only for 2 bolt mains, the RAM IV used 4-bolt caps and most RAM AIR III I've seen used 2-bolt caps with the block being drill for 4-bolts. I don't have a lot of experience with the 70 blocks. Your enigine should have 13 heads on it from the GTO. Either way it's a great block to have. And you can buy 4-bolt caps for it.