engine ser# and model application help

so I was looking for my serial and model numbers today so I can get ready to purchase my overhaul kit but cant seem to find any place to have my model or serial...on the back left of engine...(rear blower side just under the head) I have *2A2797* then below that is a three digit code reading "AC3"...can anyone help me understand these. I believe the 2A designates it as being a 2-71 model and then the sequential number and AC3 is the application, but cant find anything to support my thoughts. another thing has me stumped is my crawler as it should be is the orange color. I believe this to be true cause of areas that isn't suspect to harsh enviroments or elements or likely to be repainted is of the orange color, but my engine has an undercoating of yellow paint that has been painted over by an orange paint. I asked the owner today if it has been repowered and he said not to his knowledge but he wasn't around much during his college years and sometime after that and it could be possible his dad had done so. I'm now wondering if this is the original engine after he told me at first it was an all original unit...(no big deal) I guess I should also mention the crawler serial number is "HD5B 5088" I got that from the right rear upper section just under the fuel tank and I have already been told that the crawler is a 1949 ...thank you for all helpful information

Some AC crawlers also have it stamped near right hand final drive, too...