How much is it worth? I've done some homework recently on vintage Mustangs and bought one 16 months ago. I'm not an expert by any means, but here's my best estimates:
The first Mustang...may be worth $400 to $550 as is. If it were restored with NOS Mustang parts, it might be worth $500 to $700...and maybe up to $800 with an original color paintjob. If it were all original parts, refinished in a stock color, it might be worth $875 to $1000. But stripped as it is, even with original parts, it will be worth less than an original color refinish.
By the way, I prefer natural finishes and really like this one. That wood looks like it could be Mohagaony-stained Poplar but if it's true Mohogany rather than the more common Poplar...that's rare, and offers better sustain. And could add $100 to the as-is guitar value (or up to about $250 on an all-original Mustang).