Scag sthm engine eating oil

I have an older scag sthm 61" with a cv22 kohler command engine with about 1300 hours. . I have been fighting gremlins over the past years with it and getting by. The newest thing is that I was losing power and once I shut the pto off the engine reved right back up to speed. Now she is blowing blue smoke and eating oil like crazy. I took the plugs out and the left side was normal, but the right side was full of black crud and soot like stuff. I turned her over and e left side had good compression ( sucking my finger in and out) but the right side had notably less. I am assuming that there is excessive blow by on the right head and need a rebuild. Do they sell an engine rebuild kit? What am I looking at for cost? Is it worth the cost to have it overhauled?