Re: Head Gasket
That's one part they NEVER changed. You can look up any year Chrysler 75-85, or any year Force 85. It will cost 45 bucks at the merc dealer. 26 bucks and shipping from WISECO. 1 800 321 1364. Sierra may be the same. I think Sierra is at NAPA stores.
There is usually a reason for a blown head gasket. Be sure to carefully check the head for warping, and the sealing surfaces of the head and block for damage. Manual says you can mill .010 to true it. You can actually go .060 without piston interference--but the increased compression ratio may raise the octane needs of the engine.