There is a correct way for tightening lifters and it isn't "Just tighten them down" that's a good way to do serious damage to the engine. Some of that damage would include burt valves and damaged valve seats.
First thing to check for is exhaust leaks. Check around the manifold where the meet the heads for any dark areas that are being stained by exhaust. Will have a Flat gray to dark gray apearence. Putting s flat blade scre driver in the edge will change the sound of the noise.
The passenger side manifold is prone to warpage on Heat riser set ups. A heat riser is a flap in the passenger side exhaust at the down pipe. When cold (at start up) the flap closes and forces the exhaust back through the passage in the intake and out the diverside manifold. This is to preheat the carb to help get the engine running when cold. Some of these flaps are controled by a BiMetal spring on the flap some are controled by a vacume pot on the side of the engine.
This tends to build heat in that manifold and sometimes they can warp causing the seal to fail. I would suspect a exhaust leak there or where the down pipe heat riser and manifold meat. Sometimes the bolts will back off and it will leak giving a poping/clicking type nosie simular to what a lifter would sound like if it did not have the proper preload.
With todays' oils and proper changes stuck lifters are rare. However stuck valves are not with all the crap they put in gas these days. Vehicles that sit or are short tripped sometimes have this happen. The gas will get stale and the chemicals will start to carbon up the valves since they don't get run hard to burn it off. If no exhaust leak then before ripping into stuff try running some "Top end engine cleaner" through the truck. It's available at any GM dealer. That stuff works wonders and may cure the problem. Regardless it will not hurt to run it through and clean up then intake system. Plan on replacing plugs after wards. Mariginal plugs may give it up and start missing after a treatment.
If it still persists then it's time to check the valve lash / lifter preload. It would be best to buy a shop manual. even the cheapo Haynes for $14 at most parts stores covers adjusting the preload. Folow it step by step. I have done this a few times on various cars and I always have the manual in hand and follow it.
I don't need no damn shop manual, I got a pornographic memory.
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75 Jimmy, Dollar
Grim-Reaper
