Echo Romeo
I have looked at the DR500 but it offers very little more than a standard DR400, I think that for cruise performance all that is needed is 160HP but for lifting loads from short strips 180HP is required at take off.
The best compromise that I can see would be a CS prop on a 180HP engine, 200HP is too much power for the airframe in the cruise and the engine costs about £4000 more to overhaul than the 180HP
IO-540
B & C build an alternator that will fit onto the vac pump pad, I think that they have also an STC to replace the vac system on the PA32 with electrical gyros.
Solid state electrical gyros (both AI & DI) with battery back up will soon be available from major American manufactures fully certified.
My ideas for a "Super Robin" are based round the availability of Robin airframes that are coming up for major overhaul (re-covering) and have 1970's instrument fits, I would intend to junk all the engine indicators and fit a modern American indication system that would have product support into the foreseeable future