I would be very hesitant to mount a 4-stroke on one of the old 70's/80's era pattern ships, simply due to the relatively small size of the airframe and wing (usually around 650 sq.in. compared to the larger, late 80's/early 90's designs around 750-850 sq.in.). These older ships were never designed or intended to have that kind of power or WEIGHT in the nose. As such, the plane becomes very noseheavy, needing lots of balancing weight. This aggravates the already high wing loading problem caused by the 4 stroke's weight. These old birds will fly very well on just about any 2 stroke .60 you can put in them. With a 4 stroke, extra tail weight, and limited wing area, they would fly like a brick and be pretty unforgiving.

But, this is my opinion. Do what you will. I'll be the one standing over on the side saying "I told ya so!".

Rick