Firewall recess necessary with fixed pitch?

Is the firewall recess on the 9A only needed when using a constant speed prop? I am going fixed pitch. I also have a 90 degree oil filter adapter but don't know if that matters at all. I am going to insulate the firewall and would be much easier without the recess. I know some will say put it in just in case, but I have zero plans of maybe going c/s someday.

I recommend putting it in. It's a little more trouble now, but much more difficult later. You may not be planning changes now, but I promise you, if you don't allow for it, it WILL happen.

A little more working room behind the engine is always welcome.

+1 do it now!

You will need it for the heater cover on the inside. Besides it comes preformed and is easy to install.