Thanks for writing......
The jett alumuim mounts are available for the FIRE 50. You should specify the engine when ordering. The actual QM40 mounts will not 100% because the mounting bolt locations are slightly different on the QM40 engines.
The SJ76 and SJ90L mounting patterns are the same as that of the OS61/91 engines. Any mount you find for those will work. There are a number of soft mounts, glass filled and aluminum mounts that work well with the big-block engines.
Tower usually carries the actual OS aluminum (pre-drilled) mounts for the OS 61/91 ..... those are pretty good.
On a few of my projects I have used these
http://www.horizonhobby.com/Products...odID=HAN242024
These are not too bad either, if you want flexibility in location and engine choice
http://www.horizonhobby.com/Products...ProdID=HAN2033
Bob