I wouldn't worry about the hydro or the lift cylinder. They are pretty robust on these old gals. The old mallrat I had was in pretty sad shape, but with a running motor it worked okay.
The pics on the website show the block in a huge bandsaw cutting it down... Then you have to weld something... It looks pretty daunting. And again, I'm kind if stumped as to why, but if I had to guess, you can probably get .34 extra HP out of a converted block (And have a winter project)You can see here that the base of the block itself is too wide though. Can't bolt a sump style oil pan to it which means the engine will sit too high for the driveshaft in the back and the PTO pulley in the front. I don't see how puller guys could modify it to work. And like you said, why would they?
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Awesome! These things are pretty robust. The Dana 30 pumpkins should be the give away...Your prediction was spot on Drafter. I worked the 140 fairly hard for an hour with my stoneboat and the hydro worked A1. Needs some adjustments but don't we all.