2 grand is too high for a late 70s 75 horse. I think you'll be much happier with something newer with oil injection (and power tilt/trim, if that doesn't have it).
I'd be leery of the 'total rebuild' of that motor too. I imagine it would be spruced up, but I'm betting it wouldn't be stripped, and the block sent to the machine shop for honing, etc. At least in my part of the woods, a 'total rebuild,' coming from someone who is trying to sell a motor (especially someone who works on them), can mean a whole bunch of things.
$80-4ga. Wire
$80-14ga. Wire
First off, where are you pricing your wire from? I've found the best prices on good quality marine wire to be from genuinedealz.com. Also, I'd run your numbers through the technical calculator that website has (top of the page). I'm thinking you might be more in the range of needing 6 gauge, and 16 gauge, depending on what your setup is. $160 just for wire (without accessories) seems a little high. I've spent as much as 170 bucks on marine wiring, but that was for an electric only rig with 3 24v trolling motors, with a very *difficult* battery arrangement (3 in the stern, 3 up front, with each TM needing pairs of 2), as well as having to to extend charger leads from a 3 bank charger (no, that couldn't be mounted near the batteries, either), and that included buying the major terminals and whatnot in the same order.
Just trying to save you a few pennies where possible (because you will need them later, boat mods tend to nickle and dime you to death, especially when going all out like you are).