Well, the spinner now fits the Oliver crankshaft. Yesterday I received a stainless steel bolt 1/4"-26 BSF in the mail. Just like on the crank, the bolt only entered the spinner a couple of turns. So i filed a cutting edge in the bolt (see pic) and with gentle force it went into the aluminium spinner all the way. The amount of shavings were very little. Then the spinner threaded onto the Oliver shaft without force and with a very good fit.
Looking forward to starting the engine and feel the smell and sound of 50 years ago.