Those AN/APS 20 radars have certainly stood the test of time ! They were even used by the US on tethered balloons in the 80's and 90's to try and track aircraft moving drugs in the Caribbean.
It would be really good if one could be found to put back in XL500 at some stage. After all it was the reason AEW3 existed. I have an original AN/APS20 Operating Manual if you would like a copy.