You are on the right track. Definately replace the glowplug. The element in it may have been contaminated during the long storage period. Also open the airbleed. The new muffler may be creating more back pressure.
The new props should be about the same load on the engine. They will provide greater thrust than the old TF's which produced less thrust and more noise in some tests I made a few years ago.
BTW the way, I was the design consultant and test pilot for the original CG Falcons.
Good Luck and Enjoy

John W
Scottsdale, Az