I bought my A36 in 2012, with ca. 1,600 hours on an IO-520-BB with quite a bit of history. Eight years and 1,000 flight hours later, I decided to replace the engine with a factory reman IO-550-B, using the D'Shannon STC and baffle kit. I had a McCauley 3-blad prop, OK but not in great shape. In the end I decided to replace that one as well with a new Hartzell Scimitar prop. It turned out the prop governor was in bad shape, so I got a new one as well. Alternator and instrument pressure pump were replaced with overhauled units as well. And of course one always finds a few unexpected things along the way... Most of the firewall-forward equipment is now new or newly overhauled. It wasn't cheap - think around $80K for the above. The performance difference is very noticeable on take off and climb. I can't yet say anything about typical cruise performance, because I've only run it with very rich mixtures so far. I could get used to seeing the airspeed indicator at 170 KIAS. The fuel flow at 20+ GPH, not so much. Shane Vande Voort in Pella, IA (Classic Aviation) did the installation, and went on the first flight with me. Here is how that day went.