Exactly, Chett...this one is most likely beyond practical limits for most hobbyist-restorers and will consume more man-hours than most, even for the experienced.
Here's the math on this one. What's the bare minimum needed to have a legit, late-production, ST model (when the resto is completed) and what are they worth? The frame, LH engine case, head casting, seat pan and fenders would likely bring a couple C-notes; the rest is more or less a bonus. We know what a cleat title is worth, circa 2017.
This hinges on the condition of the frame & seat pan; there is no way to gauge the extent of the rust penetration from the photos provided. Without firsthand inspection, it's a gamble. Rust damage is wildly unpredictable. I've seen AZ bikes frames & seat pans that looked like they were stamped from lace doilies, after the rust was removed. I've also seen bikes that sat outside, for many years, in the upper midwest and the frames had nothing more than surface rust. Seat pans rot from the foam side; the foam traps moisture...and hides the rust. ST seat pans are thinner stampings than the later version and I've restored too many of them that soaked-up more man-hours than an engine rebuild(!).
I wouldn't be overly worried about the condition of the engine, unless one of the major castings is broken. Other than the uniquely ST head & case SN, 3-speed engine parts are a dime a dozen. And internal rust/oxidation, below the cylinder jug, is relatively uncommon.