How hard is it to change the power steering a 3/4ton 77 ford highboy has, to putting power steering off 79 ford on it. The 77 has some crappy power steering that always leaks thats connected to the front end,anybody understand my question?

Yes...You have a derivative of the old Saginaw P/S sytem on your truck. I would think that you could make a later version work as the '77 and '79 are basically the same truck. Being a Highboy though, you may have to use an aftermarket pitman arm and idler arm to maintain correct steering geometry. You may run into difficulty with the later rod ends mating the steering knuckes. You won't know until you get that far.

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