1961 Volkswagen Beetle Rear wheels run on the outside edges

This vehicle is really a 1959 beetle chassis that was made into a manx dune buggy. It had a 1100 cc motor, but I put in a 1600cc bus motor way more power.. anyway,, my problem is, I have a set of n50x15 tires on the rear, and they run on the outside edges of the the tire, the whole vehicle sets funny, sort of squats to the tires out when you look at it,, I had a fellow tell me they made a kit for the rear end shocks or bolt on part that will straighten this out,, do you know where or what I have to do to fix this,, thank you.