Need help!

I replaced the RCGF 26cc engine on my ESM P-51 with a DLE-30. Using the stock standoffs/mounts I have a larger gap between the spinner backplate and the cowling, which I can live with. My problem is that there also seems to be LESS space between the cooling fins and the firewall now. The Keleo Pitts muffler from the RCGF 26cc will not fit in this reduced space.

Further, looking at various other makes of Pitt's wrap-around mufflers, they all look to big to fit. I have about 1.5" between the back of the fins and the firewall. I did see where JTec has a "compact" 1.25" canister for a DLE-20, and they told me they could also make this fit a DLE-30.

Any suggestions here? Right now I'm flying with the cowling off while I break in the -30. But at some point I'm going to want to make it look normal...can't fly around forever like this!

BTW, I also noticed the plane was tail-heavy at the recommended CG location. Took a lot of nose-down trim. Even with the heavier DLE-30, it is still tail-heavy.