Or - maybe build a standoff from the OEM firewall. I'm looking at a Extra 300 manual and it uses a standoff to move the firewall an inch or so ahead of what I would call a normal firewall. Just a thought. Be kinda like a Jimmy Durante bulb on the end of the nose ...

On my 4Star60 - I just chopped everything off flush with the OEMfirewall. Makes engine swaps trivial 'cept for the throttle cable of course ...