David,

I think Jim might be referring to engines like the ST G60 and similar - true 70's engines. I tend to think of Rossi's, OPS's and YS's as 80's engines even though companies like Rossi have been around a long time - especially in the speed event.

A DB or UFO built to 7 lbs or under should perform quite nicely on a 55AX.

Jim,

There's is not too much difference in size between the DB and UFO. The latter has a swept wing and stab and a larger fin & rudder. The actual fuse is ever so slightly different but hard to detect at first glance. The wing construction changed slightly to a more modern building approach. I'm not sure if the airfoil of the wing also changed but I believe the chord aspect ratio changed slightly. The stab has a reduced airfoil so it is thinner and more in line with the Japanese designs of the time.

David.