I need to do this too. AFAIK it's a relatively straightforward fix, just time-consuming. Pull the head, remove old lifters (a special lifter removal tool is supposed to make this a LOT easier), install new ones, replace head.
I replaced my manifold gasket earlier this year so stripping down that side of the engine holds no mysteries for me any more, but it's just a bunch of work I don't want to have to re-do any time soon, which is one of the reasons I'm putting off replacing the lifters...
Depends on how bad it's ticking and how high you rev it. Might last 5 years, might last 5 months.
Typically with ticky lifters you can drive them gently til the engine dies from other problems. But if you do stuff like get stuck in mudholes, then start WOT runs at 230 on the temp gauge, the tick is going to turn into more serious things like bent pushrods & valves.
Engine rebuilding is a gray area to me so don't laugh . How would it make sense to put lifters on a worn camshaft, cam bearings, and most likely gears and chain? Mine needs this I think but I need a stethescope and probaly pulling the valve cover before I'm sure.
Just seems like new stuff on top of worn stuff might be counterproductive.