2 1/4? instrument holes
After a minor modification I’ve had great results with the metal cutting hole saws available at Lowe’s or Home Depot. Cut a test hole in scrap material similar to the panel and test fit the instrument. The hole will likely be slightly oversize. If so chuck the hole saw in a cordless drill, turn it slowly against a belt sander to remove some of the width from the outer teeth and test cut another hole. With a little grinding you can adjust the hole saw to a perfect fit.
Don Broussard
RV9 Rebuild in Progress
57 Pacer