"Not sure what year, but some where along the line, GM changed the threads on many/most of their industrial engines. Automotive blocks too!"
That's what I figured. In thew 80s, my brother had a '70 Nova with a 327 Chevy motor - dual carbs on tunnel rams. For an oil filter, he found a truck filter (Fram) that had the threads and diameter of a PH30 (I think that was old small block Chevy Fram part number) but was about a foot long.
Wix ... or Baldwin/Hastings ... must make a similar filter for whatever mates up to your block (provided you have room for something that long).