As Jerry reiterated, they're for alignment. As long as you haven't done something nutty like drill new holes in your flywheel, the pattern will prevent you from installing the flywheel in the 235 incorrectly. The holes are indeed drilled all the way through the flange and the dowel pins are an interference fit. The length of each pin is 1 1/8" with 3/8" diameter. Good luck.
