The old flywheel is thinner so there isn't much material for the two hub bolts...
The new flywheel has a concentric extension that the new 2 bolt hub fits over..The flywheel face is trued and is perfect 90 degrees to the crank.
The old steel hub has 2 pins to keep the prop from slipping, they are not necessary...The old steel hub holds the flywheel on the crank,the new one uses a nut..
You cana't see the 2 roll pins in the new hub, they're under the prop washer...Most get pulled out so no extra holes in the prop...
Use the old steel hub if it's true enough, just cut the pins off...DO NOT try to beat the pins out with a hammer, they're really tight and the crank is easily bent...
If you use the steel hub put some Loctite on the threads so the hub won't unscrew when you crank the prop....