I too have that box in my auto trans 510. I didn't know what it did either. I had to unplug mine because it was clicking really loud when I was in motion.
I know you said cheap, but I have a set of Konig Rewinds, 0 offset, 15 x 7, graphite w/polished lip, I ran on my 69. They have 195/50/15 kumho ecsta tires on them. I've got them on craigslist right now $500. Just a thought. :D
That is cool, hope he sends you some pics. We have 3 running around up here. A burnt orange R34 the guy bought it from the guys who did Need for Speed Underground 2, it has 19's, tv's,NOS bottles, mainly a show car. There is also a R32 and R33 that run up here at our dragstrip. Both very clean!
That rust looks about like my 68 4dr does, hate to see them get that way.