Hi
don't worry about the power hurting the back end you'd probably be surprised what that tractor would take in short bursts

there have been a few different motors added over the years, seem to remember about guys putting an older 6 D fordson and other perkins engines in.
Why not go 3 cyl turbo. would make it a pocket rocket. Had a MF 135 in college turboed it would spin the tires, from standing start if the yard was wet

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I seem to remember guys saying that the bonnets a pig to extend if going more cylinders. It is tapered so you can't cut and weld 2 bonnets easily like with the major conversion

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I guess the other thing is that you need front axle mountings on the oil pan, or would have to fabricate supports from the back forward to carry the axle

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Try searching youtube and see whats on there for ideas, I think there is a p6 perkins Dexta on there in the back of my memory when searching for something else
Regards Robert
A Fordson is for life not just for Christmas !.