Here's something I read on a Ford forum, found through googling, when I was concerned about crank keyway when putting my engine (non blown) together. It gave me reassurance that the key didn't really matter!
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We used to experience these types of failures years ago on Chevrolet small blocks when we would use GMC blowers on the engine. The solution at that time ended up to be using a Chrysler sized snout (1.530" Dia) on the chevy cranks. The solution usually came with a double keyway. The double keyway existed because those of us with the Chryslers wanted quick and easy way to remove our lower blower drive hubs. To effect the easy removal we would hone the ID of the hub to have a very light press fit on the crank snout. We would also use double keys but our keys were 1/4" hardened or for those of us with access to it, tool steel. Our lower blower drive hubs were made out of premium billet steel material so we had a lot of strength to start with.
The final touch was the fact that Chrysler used a 3/4 x 16 snout bolt that, in grade 8 form, reached proper bolt stretch at 380 ft/lbs of torque. Very few of us (that I knew) ever went that high. But and here is the important point, at anywhere between 150 and 200 ft/lbs of torque nothing but nothing moved. The clamp load was phenomenal and it was the friction from the clamping load that actually secured everything on the front of the crank.
from:
https://www.modularfords.com/threads/184...r-balancer-here