Building a wd45 puller

What cube can a guy get for the best bang for the buck. I am building one this winter and just would like some friendly pointers on what works good and why. I may still use it in the field if possible or else oh well. Just want alot of HP and half way reliable for farm stock or improved farm pulling

If you truly expect it to be able to "farm", your compression ratio can't be over 8.25 to 1. Anything more than that and you'll have to but higher octane fuel. Start with a D-17 engine new enough to have full flow oiling on it and install 4 inch or 4 1/8 pistons that are truly 8 or 8.25 to 1 compression. Have the cam shaft reground to "175" specs. Install a larger carb and make sure the manifold throat will accommodate the throttle plates bore diameter. Use a D-17 2,000 RPM high idle governor spring. Set your ignition timing to 22 to 25 degrees BTDC at full throttle and go. It will make some pretty good HP and be able to farm with it too. The LeRoi head is useless in my opinion for what you want to do.