I did rebuild my Super 55 gas engine. I used 3.75 sleeve kit, late 550 head and manifolds and a carb from an older 88. I spent a lot of money at the machine shop on the block. I found a poor repair on the front main bearing when I removed the crank. It had spun sometime before I bought the tractor and had a poor quality repair. I used another main cap and had it line bored. Also had to install sleeves at the bottom of the block where the cylinder sleeves O/rings fit. Also square decked the top serface of the block. The M&amp;W sleeves were too tight in the new block sleeves so that needed to be machined to fit. Had the 550 head milled .100. Did a port and valve job here at our shop. Ported the 550 manifolds here also. All new valves and springs. Shaved some weight off of the governor and adjusted the linkage to get 2600 RPM. Run 93 octane gas and 15 degrees base ignition timing. Didn't get to dyno it yet, hoping for about 50 hp @ 2600. It pulls really well for a little tractor with 28 inch rubber, lots of fun. I also pull my Super 55 diesel, shows a lot of smoke, fun also. <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->  <!-- s:wink: --><img src="{SMILIES_PATH}/icon_wink.gif" alt=":wink:" title="Wink" /><!-- s:wink: -->