I used several of those square ones with a hole in them. I stacked them and used a Sheetrock screw to mount them to the firewall. I put everything together, then set them on top of the firewall till I achieved balance. Then took off the cowl and mounted them. It turned out good that way and they seem to stay tight.

I think this adds to the stress on the gear too.

I'm still waiting for my Robart gear to arrive to get mine back in the air. I ordered new mains too from Tower. I'm going to fit the ones Stock Number
LXUX08 to my bird and see how they work.