I used a hole saw to make 1 1/4" plugs I bolted them to the standoffs and put a spot of hot glue on each side to keep them centered on the standoffs.

I used a tape measure to center the engine in the cowl, and slipped the cowl off and CA'd the wood standoffs. use them to drill the firewall.

A hole in the cowl needs to be cut to clear the DA-50 head.