The shocks I tried are HD part number 54635-09 Touring Low Profile Rear Suspension Kit. Maximum pressure: 50PSI (345kPa). The effective air spring size is too small so the higher pressure was needed to hold the weight of the R3 and me. With this much pressure the progressive rate is very high (they get much stiffer with very little travel) so the ride quality wasn't good. The installation instructions recommend 15PSI (about 104kPa) for a 225 (about 103 kilo) rider and 50 PSI for 300lbs or more on the HD. So yes, to use these on the Rocket you are way,way over recommended pressures. I, too, thought they might be a good solution for changing between solo and two up with luggage riding but they are not good for either.
I now use two different shock and spring setups for my R3 and switch between them.