Well, yes & no. If you're just talking about worn valves & valve seals on a single cylinder (with the assumption being that the others are also worn but just not to the same degree) then no, what you're looking at is just swapping the heads. Get yourself a set of rebuilt (or low milage junkyard) heads and swap them out. If you're not familiar w/the process read up on it and ask advise but it's something most folks can do. Really though, read up on it. First time I swapped my 460 heads I didn't realize that a couple of the bolts passed thru water-jackets & didn't seal them which led to no end of head-scratching afterwards. Once you feel comfortable with it jump in and swap them out.
Now, as for the "no" part of it. Maybe there's a miscommunication between you & the group or you & the mechanic but as I read your post it was my understanding that the valves on #8 were *bent*. Quite frankly, that's a whole diffferent ballgame. If they're bent then obviously something CAUSED them to bend and before you slap on another set of heads it would behoove you to find out what wrecked the current ones. There are only two things coming to mind right now that would actually bend a valve. One is piston slap & the other is hydrolocking. If you hydrolocked the engine then you somehow got water (or some other incompressable medium) into the combustion chamber (usually done while crossing deep water or doing something equally foolish) and when the piston came up something had to give. The other route to a bent valve is slapping it with a piston and my only experience with that has been with a *very* stretched out timing chain that had actually jumped a couple of teeth. With 155K it's not inconceivable that that is what happened. Either way if the valves truley are bent then it really is in your best interest to find out what bent them before you replace the heads. If you slapped the valve then there's also a good chance you flat-spotted the bearing and a smaller chance that you bent the rod.
I guess the short version of what I'm saying is to be very sure of what you're dealing with before you shell out the $$$ for a new/rebuilt set of heads & invest the time, labor & bull$hit in changing them because if you're anything like me you're going to be more than a little angry to spend the cash, do the work & then listen to the bearing rap when you fire it up.
what if i just bought a set of heads and did the work myself? wouldnt the truck run fine after that? Or is their other work involved when rebuilding the heads??/ thanx