[BCreekDave]

The 3970010 actually doesn't mean very much. That was a block they used in both 2 bolt and 4 bolt configurations from 1969 through I think the early 80's in both cars and trucks. There were probably more small blocks with this casting number than any other.
The ACRE 10232 is pretty much meaningless in terms of factory stamps as far as I know. Probably an engine shop stamp. The cut marks on the pad are definitely wrong too. The factory broached the head surfaces on the block and the marks left from the broaching process look totally different.

There is a casting date code at the rear of the block on drivers side top near the bellhousing. It will be of the form LETTER-THREEDIGITS where the letter is the month and the next 2 digits are the day of the month and the last digit is the year. Post those and we can at least decipher the time when the block was cast. The casting date should precede the cars TT build date by as little a 1 to as much as 4 or 5 weeks generally. As an example, my car has a 04B TT date and the block was cast C230 or March 23rd, 1970.

There is VIN number stamped near the oil filter on the block by the bellhousing. It is very hard to see as its on the rough casting, especially while its in the car. This would be the gold standard to tell if the engine is original to the car. I had to photograph mine from various angles with both a flash and no flash with my iPhone to make out the letters. You may need to take some lacquer thinner to remove the paint. Don't use a wire brush!

Still sounds like a nice car. Can you post more photos? The TT indicates a deluxe black comfortweave (712) interior.