RE: Changes?
Lunbom,
The Fox engines you listed would definatly benefit from some castor in the fuel. They are lapped iron piston and sleeve type engines. The castor buildup on the piston helps create the compression seal.
Most of the popular 2-stroke fuels contain a fair amount of castor and should be suitable. As added insurance, you could always get a pint of castor and add a few ounces per gallon (of a two stroke fuel) for the first dozen runs or so to help with the break in process.
To get any longevity and user friendlyness out of the listed Fox engines, some castor is necessary.