Instead of using washers I made up strips to sandwich in the 3/32" thick silicone cowl seal material. Used construction paper to make the template for the strips.

Used left over .020" and .025" 2024 aluminum. Here I've clecoed the hold down strip in place. A lot of trial and error fitting. May have to redo the baffles again in order to get the proper fit. I'm not sure how much the engine moves on the mounts. I was shooting for a half inch space.

Here I tried using the silicone P shape seal on the rear fence. Didn't like the fit. Went with the plain flat silicone material.

Here I piled up everything I had made up firewall forward to try to get an idea of the firewall forward weight. 163# without exhaust. Used 2 scales with my son and I holding the engine and standing on the scales. Not sure of the accuracy.