Hey Greg. I'm looking for a couple 500 or 518 units. I had a A518 out of my 91 van that a sold to my friend a few years ago for his 70 Cuda vert. Now I wish that I would kept it. That unit was a 2 wire meaning no lock-up converter. I pickup a A500 and an A518 but both are 3-wire using as lock-up converter. I'd rather had the 2-wire units. I found a couple 91 vans in a yard this weekend but one was not an OD the there was an A500 3-wire which I already have so I didn't get it.
Keep checking to pick a part yards for 88-91 vans and 2-wd trucks. You can snag one for under 200.00 with the convertor. They are getting harder to find.