Yes, you're block is drilled for a ball stud for the Z-bar. I also have a 403 engine, all fresh with the same recesses. I would NEVER cut the "snount" off the main input shaft. I thought about getting one of those "sneaker" pilot bearings and mocking it up to see if the 403s "triple" recess is deep enough. I'm not a fan of drilling a "clearance" hole to use the sneaker bearing either. I personally would only use the sneaker bearing if the "mockup" had clearance.
My thinking is if the sneaker bearing doesn't work out, due to the bearing recess hole not being perfectly centered or the bearings don't hold up, etc, your going to have to pull the engine and machine it properly for a factory type bronze-oiled bearing.
Rather than do my 403 that way, I'm changing directions, for now.
Last Wednesday I dropped off two 425 crankshafts and one 455 crankshaft. One 425 and the 455 are already machined but for automatics. The one 425 is std/std perfect crankshaft. Hopefully it'll work out. I told him a lite polish will be fine clearance wise if needed.
I gave him the Mondello pilot bearing drawing. Good luck.