When you install the ply sheeting to the front add a few toothpicks into the sides of the firewall. on both of mine I needed to move the firewall back an inch for the OS gt ​​​​​22 engine so I remade the firewall to fit and put triangle stock on the front and rear

firewall moved back 1" on j-3



trailing edge beveled stock in corners

ply extends onto edge of firewall on L-4


cowl mounting in ply before triangle stock installed, I added an extra layer of ply for blind nuts to attach cowl