Go for it! I have e few reasons to say so, first of all I took a good long hard look at the pics, and it doesn't seem so bad. There's a lot of growth on it (Do you call it algie?) which would clean right up with some industrial soap and a pressure washer/steam cleaner (NOT the domestic "clean your tub without acid" kind

) Second there's some rust spots on the tub, but nothing you can't fix, the frame looks ok, with original paint still on. Here in Denmark cruisers that old are either totally covered in rust or restored 2-3 times.
If you don't it will always be the one that got away!
Lets say that everything goes sour, then you have wasted 800$. As for old car experience I call that a cheap tuition fee! But you would know what you did, and you tried. If you let it go, then it would have been the project of your dreams years on, and you might regret it forever!
You have the girlfriend on board, and that can be the hardest part about old cars, I'm fortunate enough that my girlfriend loves old cars as much as me, we are lucky!
So all in all, full steam ahead, we only live once!