halfwound121:
I know there's a system for figuring out the date codes, but I haven't taken the time to learn it. Not an exact science, I would imagine. My '76 and '78 necks are both 1-9/16". I have a JMJ neck (Repro of Justin's '67) that I bought for a project and an original '67 bass that both have the chunkier 1-5/8" necks. The '78 has a maple fingerboard that I'm beginning to think I like better than the RW. What's the body and pick guard color on your '74/'75?
FWIW, I recently discovered something else about the vintage Mustang basses, which is the differences in V/T knob designs. The '66 through '75 models have the simple Jazz type knobs with fluted sides and the single white line indicator on top. The '76 through '81 models have skirted knobs with white VOLUME/TONE lettering on the top and white numbered level indicators on the skirt. All the later models appear to have returned to using the simpler Jazz knobs. I like the skirted ones better.