If that 25cc Homelite conversion weighs 64oz. you don't want to put it in a 72" Extra. It's way too heavy. You need to stick with glow or buy one of the lighter (read more expensive[]) gas engines. The Brison 2.4 may be your best choice: low weight, good power, great running, and a reasonable price. Good luck!

p.s. Just for comparison, my Brison 3.2 with pitts muffler, ignition, and battery weigh just a few ounces more than that bare Homelite conversion...food for thought.