Vintage Cars: engine code for general motors, 1969 pontiac lemans, distributor hole

Question
i have a 1969 pontiac lemans. i am having trouble identifying the engine. the stamping on the passenger front is 590391, or possibly 590891 with the letters xh underneath that. i believe it is a 400cid, but not quite sure because i cannot identify the codes for the nemerals.
thanks
brian

Answer
Around 1968 Pontiac also stamped the VIN numbers next to the timing cover about even with the timing marks on cover. is that what you are looking for?
that XH means  - should be 400/350HP engine - specific for 1969

I also found this information posted by a cyber buddy of mine

Pontiac used the same codes on different year blocks.To differentiate them it will have to be determined what year the block is.Next to the distributor hole there is a casting number that has a letter with 2 or 3 numbers. The letter is the month of manufacture- A=Jan. B=Feb,etc.

The next number or two is the day, but sometimes the factory left the first part off, i.e. 5 could mean 5,15,25.The most important is the last number,it is the year of Manufacture it is not always the model year,as most blocks are cast a few months before the car is made