Were it a 550 those overbuilt heavily sprung inexpensive ones that ran about $70 around 7 -8 years ago might fit the bill. They might have been 750 or 550 shocks...don't recall. Or a good set of Goldwing shocks which are an inch longer than stock 750 shocks. Have a set that were painted black I haven't tried. They were deemed by most to be too harshly sprung and don't recall what was said of their rebound and dampening control other than save you money and pass on those shocks.
Given your big bottom girl you may wish to pick up or borrow a good set of Wing Interstate shocks to try. The Silverwing were air assist by 83 and GL650I. Motor Era may have info or several of the Wing owners on the board may be able to help or advise you. Would not suggest the GL650I shocks as by '83 the ProLink Mono-shock was being used....
Don't think you are looking to re-engineer the rear swing arm and subframe to adapt a ProLink or Monoshock setup on the bike. The GL650I was a very soft comfortable ride but lacked ground clearance unless aired up and then it was comfortable but still soft, as intended.
BankerDanny, DonR, DHall are just a few of the wing owners I can think of off the top of my head...