704 combat is what used to be in the AMA rule book for scale combat (.15 sized engines and 1/12 scale). This goes back to I think early 90's. It is no longer. Scale combat today is flown to AMA 2610 rules which in a nut shell allows engines of .26 cid and below and a 10% deviation from the 1/12 scale deminsions.

There is all the info you could ever need on all that is combat here:

http://www.rccombat.com/rcca.asp