Hello, I could not find a thread in the forum for this and nothing I have found in engine code sites have been able to identify my block.
I have a 1969 GTO. It was built in Baltimore in October 1968. I have the dealer order sheet and from what I could decode from that and other items, it seems to have been a down option 2 barrel 8.6 compression 265 horse motor and it was originally an automatic. The block code is XM, but I see little evidence of other 1969 identifying marks on the block. Here is what I can decipher:
1. There is no transfer lug and it has 3 freeze plugs on each side
2. The date code on the distributor pad is L217 (which tells me the block is from December 21, 1967) - I know XM was used in 1968
3. I do not see a year marking next to the distributor (I have a modern GM HEI distributor and it is hard to see in there), BUT if this is a 1968 block, there would be no year noted by the distributor, right?
4. I do not see a casting code near #8
5. On the front side of the engine block, on the passenger side - in front of the first freeze plug, there is a casting GM 10
6. Above the XM stamp on the front of the block the number 337397 is stamped. I am sure about 337, but the 397 is questionable
7. On the front of the block, down near the bottom of the timing cover, there is a number 287116193 - I am pretty sure I can see that right
In case anyone asks, the heads are cast 48 and the date code on them identifies them as being cast in August 1968
I suspected that the engine in my car was not the original even though I was told by the prior owner that it was. But, is it possible I have a 1968 block in a 1969 car and it is the correct block? or was Pontiac careful to not cross model years? Is it possible that early in the car's life the block took a vacation and this is a GM replacement block? That may be why the previous owner thought it was the original block.
If it is a 1968 block, that would explain why the normal 1969 identifiers are not present, but the GM 10 stamp concerns me. It's definitely a Pontiac engine - it has a windage tray.
I am getting ready to pull and rebuild the engine. Then I can get a better look at markings, but I thought I would ask you guys what you think first.