I changed the front wheel to a 24" one (had to cut the brakes assembly off to do this and patch the fork and grind things smooth again) ... and rode it around. Pretty nice. Then I changed it to a 26" wheel (the brake assembly was still off). It rides pretty good and is the same size as the rear wheel. Which means you can theoretically make it from just one donor bike.
sideview with the 26" wheel
Brakes removed
sideview of the front fork
Wheel clearance of front fork ...
too close for caliper brakes,
awkward even with "V" brakes
Another view of fork clearance
This view shows the roller for the return chain.
It keeps the chain from swinging back and forth and wreaking havoc. I had to drop it down a little so that the chain didn't rub the bottom of the frame when on the big gear in the back and the big gear in the front at the same time.