Some simple fixturing could reduce the risk of drilling and tapping in place.

When drilling and tapping by hand a tool that helps a lot is a guide block. We had them each tap size to keep the tap straight. Most times we made these ourselves on a mill.

The same basic tool for the crank could be made on a lathe. One end pilots on the crank snout and the other guides the drill.

By using a bushing on the drill end you can can use the same tool to guide the tap. Drill bushings are an off the shelf item and are made of hardened steel.

Kevin

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...