The only folks running roller rockers are the race crew. There is friction to be shed there, but you will find it is at engine speeds that you won't be running.
For the slant, those rockers are pretty expensive. They are only available for mechanical valve train engines.
With an 80, you should have a hydraulic cam. (If there are no adjusters on the rockers, that's what it is.) The hydraulic lifters are fed oil from the rocker shaft, through the rockers, and down through the pushrods. Weird, huh?
I do not know of a roller tip rocker that will work with the hydraulic top end.
The stock cams are pretty good, so there's not much reason to mess with them unless they are worn.
First, identify the carburetor that is on the engine. For purposes of Hypermiling, the 1bbl can be worked to deliver better results than the 2 bbl. If you are dealing with heavy traffic, and find yourself having to stand on it frequently, the 2 bbl will do a bit better. If you can't find the list or tag number on your carburetor, take a photo of it, and I'll see if I can figure it out.
The best bang for the buck is to get the best tune up parts you can install.
Get the Echlein MO 3000 rotor, and Standard CH-410X "Blue Streak" cap with copper contacts.
The Echlein caps have spotty production QC, so you can get a good one, or one that is off center. Stick with the Standard.
To make absolutely certain that somebody didn't bolt up an older head, tell me what your spark plugs look like. Are they small taper type plugs that install directly into the head, or are they large ones that insert into aluminum tubes with seals on the outside lip that fit down inside the head?
The "Peanut Plug" head is the later version, the "Drool Tube" head is the older one. For a taper seat Peanut plug head, use NGK UR4GP plugs. For Drool Tube heads use NGK ZFR5N plugs. Always remove the crush washer from the plugs before installing in a drool tube head. The aluminum makes the seal.
These plug options are extended electrode type plugs. This puts the ignition spark in a more ideal location for proper combustion. A peanut plug and a drool tube plug are not interchangeable between the different heads. Make sure you get the right ones.
Some folks swear by indexing the plugs in these engines. With the extended electrode plugs, the point is moot. You don't have to mess with it.
Platinum, irridium and all the boutique plugs aren't worth messing with in this engine. Don't mess with multiple ground strap hype or any of this. It's a low compression engine. That stuff doesn't help, and in some cases will deliver poor results.
Depending on the mileage of the engine, it is likely that the timing set is worn out. The chains have a life expectancy of 100K Miles. While you have the plugs out, roll the engine in one direction with the distributor cap off. Now roll it the other direction. If there is a lag before the rotor starts to turn, it's time for a new chain.
Now, Tell me about your distributor. Does it have a vacuum advance on it? Is the advance hooked to the ported vacuum on the carb? Have you got a dial back timing light or access to one?
Do you still have EGR? Is it working?
If you have a lockup converter, cool. If you don't, the entire transmission has to be replaced to install one. This is true of the Mechanical lockup and the electronic.
What transmission did you say was in there? The A904 costs you about 25 or 30 HP at peak power, while the A727 takes about 60 HP. If you have the A727, which would be rare, your probably not going to make the 20 mpg point. If everything is stock, it's extremely doubtful you have the 727 in a 1/2 ton of this vintage. They were more common in the late 60's heavy half ton and larger pickups.
If the rest of the crowd wants, we can move this offline to Private Messages, unless of course the crew is interested in the mileage of our dinosaurs!
CJ