mmorg1,

If the engine you have has a large heat-sink type head, it could actually be a Rossi .81. Rossi basically bored out a .61 to give them more cubic inches in the same sized package as the .61. Whatever it is, I recommend trying Wildcat 5% nitro ducted fan fuel. It has worked very well for me in the past. Wildcat has 22% or 23% lubricant, and is one of the most widely used fuels by those of us who still fly DF's.

As for the retract air tank, I fit mine in the Eagle's nose wrapped in a little latex foam.

Hope this helps. Good luck, and welcome to one of the most exciting facets of the RC hobby! You're gonna love it.

Earl