I would look at the lifters first to check for wear and inspect the rockers. If the lifers are worn, you will want to look at the cam shaft to make sure the lobes aren’t worn as well. With a little luck, you might just need to replace the lifters and be good.
Worn roller lifters in a 4.0 OHV are pretty unlikely. Odds are the hydraulic internals are gummed up. Plus rocker arms and pushrods are like $4-5 for a set of four, while lifters are $30-40 a piece.
The question is, what kind of budget are we talking about here? Parts? Labor? Time?
To the original question, if the motor is just ticking excessively, but othewise running fine, then it can be refreshed, possibly without even head work.
1. Check serp belt accessory drive for bad components.
2. Check for exhaust leaks.
3. Use a mechanic stethoscope to probe surfaces around the running engine.
4. Test compression.
If everything checks out but there is distinct valve train noise, then the top end of the motor can be removed in the truck. Plan on replacing upper/lower intake gaskets and possibly head gaskets for sure. Then from there replace rocker arms, pushrods, or lifters as needed.
- Remove upper intake & attached lines & linkages
- Remove lower intake & fuel rail
- Remove valve covers
- Remove rocker shaft and look for worn rocker arm cups & tips, and worn pushrod ends
- With the rocker shaft removed and a pushrod in the head, try pushing into the lifter. The internal plunger should move up and down with spring pressure at least .050"
- If stuck, then the heads should be removed (exhaust manifolds attached) to get the lifters out.
- The lifters can be cleaned with solvent, needle nose pliers, and compressed air. There are videos on Youtube showing how.