When I was looking for another tractor, I wanted a gas model, larger frame like the 756. I had read that some JD owners had ignition issues with 3020 and 4020 gassers - but I've never read anything about those gas engines not running on today's gas or any other tractor gas engine. Read and even posted regarding larger IH gas engines and their reliability and maybe I didn't read enough, but none the less, I came away with the feeling that a gas 756 would be the cat's meow for no more hours than we'd put on it in a year. I liked the idea of using it in cold temperatures, tooling around and no wet-stacking issues. Once I started inquiring about C291 rebuilds, the whole gas issue and you ain't going to take the C291 to the local engine rebuilder and have it rebuilt because of the sleeve issues, specific knowledge required to rebuild this type engine, special tools required, etc., I'm thinking - what have I got myself into... The C291 is the ONLY tractor engine that I know of that is plagued with these issues. The C291 is truly a POS engine.
The Cummins 5.9... I visited a friend's farm several months ago and he had put a 5.9 into a 706. He did a GREAT job with it and didn't break the bank doing it. He took a 706 good tractor and made it a great tractor. As I mentioned earlier, I don't know that I'd do a 5.9 and ruled it out prior to buying a replacement for this tractor on the farm - but I've still got the 756, everything but the engine seems to be in good working order, and after seeing that 706 with the Cummins 5.9 - I'm intrigued about the replacement again. Maybe not this year, maybe not next year - maybe never, but I'd rather roll the dice and spend the $$$$'s on a Cummins 5.9 transplant in an otherwise good tractor than rebuilding a junk C291.