I dimpled one of the HS skins and then made a hammer tool for the engine crankcase through-bolts. This is to allow the needed force to insert the bolts while protecting the threads. This little tool, made from 2" cold rolled steel round stock, weighs right at 3 pounds and should work great to provide needed momentum without any damage to the bolts. I milled both ends square and then drilled a 1" deep 29/64" hole and then tapped to 1/2-20. Spins nicely onto the bolts. One of the more interesting parts of building for me is the special tooling and their uses.