Re: New Project- Vintage Motorized Bicycle!
You can look at the tire to find tire/rim size. Old, crunchy tires might be impossible to read, but the newer (70's) ones you got should be in good enough shape to read - or I wouldn't ride em!
27 inchers should have a 630 in the size, like 32-630. Older "26 inch" tires could be a lot of different sizes. Most mountain-bike tires are 559mm by some inch width - like 26 x 2 1/4. But old road bikes had sizes like 591, and if you get the wrong "26 inch" tire, it won't fit. I don't know about 24-inch sizes.
You'll want to find out the size for buying tires and to figure out gear ratios/ rpms.
No matter what the 3-speed rear hub does, that motor looks like it could get you moving to a good speed. I rarely break 15mph when pedalling, but when the motor's on, I'm always going +20.
Keep us up on your build progress and good luck.