With aftermarket pulleys, tapping the 250 crank is a good plan because you never know what sort of fit you'll have.
I would sand the inside if the pulley down a little.
With the bolt in place, it will keep the pulley synched once it is home.
The 292 was tapped for a 7/16 crank bolt and that is the size offered via the 12-bolt jig you have.
Use a torque wrench on the 7/16 crank bolt, to ensure you don't strip the threads.
You'll want to stay under 40 PSI to be safe.
If you are unlucky and strip the threads, I will send you the jig, tap, and a washer bolt assembly, for the larger bolt, but won't be able to ship it until early next week.
It's worth noting that the factory tapped the Iron Duke 4 cylinder engines with a larger bolt, while the 3.0 liter Mercruiser engines had a pressed pulley like the 250.
We've been tapping the 3.0 liter crank with the larger bolt for years on our 4 cylinder conversions, and now tap both the 250 and 292 conversions we do without any negative effect, so there are no down side to tapping the crank.