Glad you found your starter, I just went through this with my 400 block which is a staggered starter only application. I used the Centerforce T56 flywheel which is a 153 tooth version. Had to drill/tap the inline hole while the motor/trans was installed in the car. I just contacted my machinist and he had a jig for this mod. The larger size for the knurl of the starter bolt does indeed extend into the block approx. .250". For those that go this route, you'll need to drill that portion out to .378 or .379 which is done with a metric bit, I believe the letter designation is "W". The knurled bolts are designed to fit snuggly into the starter housing and the block to eliminate any torque movement.
I went this route because I already had a mini-starter which I liked and drilling/tapping just cost me the price of a drillbit.