My car originally came with 14 inch wheels. Due to the car’s air-conditioning, 15 inch wheels were not offered. I have since installed 15 inch wheels from a 1963 Buick Special wagon. These wheels share the same part number.
I do have a 3:90 gear set up that is meant for 1963 Skylark posi, but the Jetfire shares the same posi parts as the Skylark. I haven’t installed as I thought it may rev the engine too much. Also, being in this small town, it would be hard to find a mechanic and proper tools to install it.