Re: changing lifters-is it a hard job
I've always been told to always run new on new, as once the wear pattern is established, new ones will just wear faster...new have very slight convex bottom, that will help it seat on the cam better than if it were flat as it will tend to hit less at the edge, but once everything wears in(its probably only a thou or two) the lobe/lifter lap into exact fit. a little flatter on the lifter, a bit more dished on the softer cam lobe. If the removed lifter is dished on the bottom, the cam has likely worn much worse, and new lifter may only be short term solution. If the removed lifter is not noticably dished(see if it will rock a tiny bit on a piece of glass), it may just have gummed up- theres only a snapring,piston,reedvalve-like shim, and spring inside, could easily just be in need of a cleaning(maybe a spring, but doubtful), and if same lifter goes back on same lobe, wont introduce any new wear patterns- if its dished though, in my opinion,you'd be better to just change everything and be done with it.
Back around 1980 I had a 400C in a $75 car I drove to school, had one ticking horribly- just to get rid of the noise(I couldnt even afford gaskets back then) the 400's were 'non-adjustable', so I pulled the aluminum rocker fulcrum and filed the base down a bunch to take up the lash...totally wrong I know, but it ran tick free(although the bottom end sounded a bit on the loose side) even the day I finally junked it out. That poor old motor had zero oil pressure when warm, but it made good power and never failed to start, drove it almost two years...its amazing how much abuse some engines can take.
regarding wear- I put a set of harlan sharp roller rockers in my 396 chevy(had it in a 81 dodge pickup), as it tended to keep breaking the stock ones, drove it for over 10 years everyday, pulled the motor apart to rebuild it, and found 5 of the rockers were kinda chewed up in the little steel pressed in pushrod seats- not repairable...as I had paid $200 for those rockers, I sure wish I would have replaced the old pushrods too...old on new often causes such problems.
Confidence: that feeling you have just before you realize the mess you've gotten yourself into...