Yes, the one Mark C flew to Jerusalem. I never flew the aircraft with 105hp Potez fitted, but I had a share for some years in a DR1050M1 Sicile Record: so same wing (as unmodified 1051), same fuselage and 100hp O-200.
I flew both several times from the same strip on same day; the 115hp O-235 and flaps do make a significant positive difference in performance (allowing for prop differences too), as you might expect. But the Jodel wing shows its mettle throughout, naturally.
The Horis can do magnetic heading but needs a separate sensor fitted. I've had a 57mm Horis in my glider for a couple of years, easily my favourite instrument but then I've no experience of any of the others.
Overall everyone seems pretty happy with what they chose but maybe a slight query over the MGL - for which I would have to make a new panel anyway. The GRT does look good but I couldn't find a UK dealer and I think it would be top end of price range.
I have the Avmap Ultra in my D117, it's been brilliant. Magnetic heading works fine. The 'pseudo' VOR and ADF are excellent. I used them touring France and Belgium this year as backup to SD. I agree the Horizon could just save your life crossing the Channel. There is a software update a mate did for me that makes the QNH quicker to set.