Good work!

The gold standard is really the ES machine by Wouter Strietman, since the grouphead IS the boiler, there is no issue of temperature loss/gain/whatever - similar to the saturated pump groups. Groups are away from boilers just to cool the temp (it seems to me).

Don't tell me. I have the Strietman CT1 now here for a couple of days. It's just amazing. But the group in this case is much more "isolated".I fear the heat of the boiler is just not high enough for the Pavoni group. Either it need some kind of circulation or pressure (higher temp) in the boiler. A third way could be a different (lighter) or a directly heated grouphead.

The La Peppina has a very light weight aluminum group and portafilter, some have speculated because it's an open boiler and there's no need for a massive heat sink of a group to reduce the boiler temps to brew temps. Without group head heaters, it could be a problem using large groups on open boilers.

Well, the present project will end speculation, I reckon, once it can be put to the test. There's hope, I think. Brew temperature is below boiling, anyway, and with an open reservoir you can afford to flush liberally - just add more water any time you want, unlike the routine with a pressurized boiler.

You could always drill some holes for a cartridge heater or two in the grouphead (if there is space) and run it off the same PID you would use for the main boiler. They are very cheap off of ebay.

Without digging into it too far it would be relatively easy to heat the group with electric TIC heaters and maintain the open hot water source at something slightly above group temperature. This idea has merit for the easy implementation of electronic control of brew water temperature within a narrow range.

Heating the grouphead is no problem
Its the type having water inside it
just rise the lever to the point water is ALMOST comming out, and lower again
That will push the water back into the boiler, and lowering the lever pulling new hot water into the grouphead

repeat as many times as needed

on my M model Pavoni , i had to do this two to three times depending on how cold it was in my kitchen
but NO water is wasted