i never felt inclined to read as much in my 93 helms. i have three blocks. 2 usdm2.3 and 1 jdm2.2 all of them have fitment for the oil jets and look identical to me. just diff stampings and internals. based on speculation im guessing you're right that honda adds the frm as needed on the specified applications. another piece of information is the difference in bore size. there is marked difference in the 2.3 and 2.2 hseries. another hint that honda uses the same cast for both and modifies as needed.

machinehead im sure neither of us are honda engineers...maybe further detail your research