Magnum crank and 4 speed

You're begging for trouble. If it's not rough drilled (most are), Bobbitt the tip of the input shaft off with a wizzer wheel and move on with your life. Rough drilling a crank is begging for more trouble than it's worth.

Another way to phrase it: Which is easier and cheaper to mod? Modify that.
I’ve been thinking that if I drill the crank, it will through the balance off.