For what it's worth; I also have a '77 Trillium
4500 (sorry David, I'll get details for your database to you soon) with a straight axle, leaf springs and shocks. A PO had made the conversion to enhance ground clearance (as it was explained to me). It now sits a mile high and bounces all over the road. The frame was chopped up a bit to accomplish this, but is well braced and still pulls very well. I expect to replace the axel next spring and convert back to original revised specs (torsion, trailing down angle, 2500#).
I don't know if there was someone that specialized in these early conversions. The sad fact is that clearance was only gained at the front and rear of the trailer (which may be what they were looking for), but with 13" tires
, the straight axle would still have hit many of the same obstructions.
I'm hoping that with a new torsion axle with a slight rise over stock, I'll be able to use 14" wheels and tires
and gain some ride control.