I have a few photographs of the Heron with an engine removed which shows good detail of the firewall etc. Plus a few others. They are in BNE. I'll be home on the 4th of next month on leave and can email them if you pm me. The IO-540 engine was 290 HP by memory (PA31 engine without the turbocharger de-rating it from 310 HP) Even on a hot day with a full load they performed better than most light twins. Very 'Pommy' though, rivets from a shipyard, phneumatics, rag flight controls and a cockpit that looked like a madmans tool shed.