Hi, thanks for writing.

I am sure a SJ-120 combined with the stock Jett-Stream would provide some major pull on an H9 Mustang, but it would require a bit of experimenting with props to get the speed you are looking for. The engine is designed to run in the 9500-10000 rpm range.

There is a Turbo-Jett in-cowl tuned muffler available for the engine that will provide excellent performance.

I would caution, that this is a LOT more engine than recommended by the manufacturer for the aircraft.

These links may be of interest
http://www.jettengineering.com/hall/at6com.html
This AT-6 racer is powered by a SJ-120/turbojett combo.

http://www.jettengineering.com/engines/sj120dub.html
Dubs comments and background on the 120

Keep in mind, that the 120 is the same mounting dimensions as the "60" big block engines, but is about a half inch longer, and a bit heavier.

If weight is a concern, you may also wish to consider the SJ-90L or BSE 90 which are lighter and designed for a bit higher RPM.

I hope this is helpful.
Bob Brassell