When I brought my 78 F250 snow fighter home last week the clutch just gave out on me. It's got a 400 and NP435

It still holds the engine and transmits power, but It won't allow me to shift. The pedal is limp.

The ninny that had the truck before me put a mega body lift on it. Rather than lengthen the rod, he lengthened the cam. This gave it more leverage and I'm guessing thats the underlying problem. I'm removing the body lift first. I will bring the linkage back to stock too. Other than that the linkage outside the bellhousing looks good.

I have the factory service manual (NOT chiltons) and it covers so many different clutches that it's not helping a whole lot.

My gut feeling is, just take it all apart and replace it all.

What size clutch am I likely to have?

Who's got the best replacment parts?

It should have a 12" clutch in it. If it is still holding power, but not shifting, i would be suspect of the fingers of the pressure plate being broken/bent, or the throwout bearing is junk.