The Mac is probably a 32cc. Pull the muffler off of the Homelite. If you see a "bridge" in the exhaust port dividing it in two, it is a 25cc. If there is no "bridge" in the port, then it is a 30cc. If the Homelite is a 25cc, in your position and capabilities I would convert the larger Mac. If the Homelite is a 30cc, I would convert it instead of the Mac.

Good luck and have fun,
AV8TOR