How I did the appx 8 inch dia fiberglass cowl on my DR1:

Mounted the 4 blocks to the firewall as per instructions, lined the rear edge of the cowl with foam weather-strip (Lowe's) drilled the cowl for the #2 wood screws and placed it on the plane. inserted one screw at a time, drilling the wood mount and tightening the screw to slightly compress the foam BEFORE DRILLING the next location. (I started with one of the uppers, then the other upper, to reduce the potential of twisting the cowl to one side in this process....)

I have to put the screws back in in the original order every time, but the cowl dowsn't move at all, and has shown no signs of any wear or cracking in appx 25 flights, with most ending in a nose-over. (darn Dr1 LOVES to nose-over )