Thanks for the responses. I think I found a place that has the old old lever assembly. It is https://www.coachsupplydirect.com/rv...l-slide-cable/
. I talked to the guy there and he said he had a few of the old old design. The old old design (as opposed to the old design) has the screw holes diagonally across from one-another, while the old design has them centered one on top of the other.
I couldn't get just the lever box; I had to buy the lever box and the cable. Hence, the price is $35 plus shipping.
I also contacted KustomFit, but they had only the old design, not the old old design. They said to just drill new holes in the chair, and were only $25.
Working underneath the chair is very difficult, but I did find a way to release spring tension, using vice-grips to grab the tension spring and slip it off its seat frame anchor point. With tension released I was able to slip the cable out of the groove in the lever box, then unscrew the cable out of box. I haven't installed the new lever box yet, but I hope I can use the old cable. Otherwise I may have to remove the seat to get at things. The seat is bolted down with 4 bolts that extend into the fender well.