Gas/Glow would work find used with ignition, though it somewhat defeats the original purpose of Gas/Glow, which was lighter overall installation, and cheaper.

And yes, it would add some power. Most of my Gas/Glow engines showed at least a 200 rpm gain, which is definitely noticeable on a 16 to 22 inch prop.

Nitrous Oxide wouldn't be very practical both because of the heavy high pressure tank needed, and the limited duration of the boost.

Tuned pipes work quite well on gassers and usually add 800 to 1000 rpms. Look into Macs Products. They have headers, tuned pipes, etc. for many engines. There are other sources too.... They aren't often used because they are long and bulky. Looks like a torpedo strapped underneath the plane!

AV8TOR