Rebuilding a (stock) 340 for my '71 Challenger. I noticed that two of the lifter bores have a bit of slack when fitting new lifters. I don't have a measurement yet, but lifter can rock back and fourth ever so slightly in bore. Can I let this slide or do I need to have them sleeved?

Was the engine running prior to the rebuild? Measure them. If the lifter to bore clearance is greater than .002 I'd look into having them bushed. You also might want to measure the lifters to make sure you don't have any of them on the small side. If you are using a modern grind cam and something with a little pop to it, that lifter to cam lobe orientation is very important. If this is a stockish type build it's probably not a big deal.

that does not sound good. What Moper said, get a carefull measurement & post what it is

They used to sell oversize lifters (at least mopar did).
http://www.moparpartsgiant.com/parts-list/1987-dodge-diplomat/camshaft-valves-5-2-l-engine.html

I did a search and in this post they claim Don at FBO will sell oversize lifters. read on http://www.forabodiesonly.com/mopar/archive/index.php/t-254810.html

They used to have oversize lifters. Not sure if they still do but that would be a choice too.

Do you have a 'diamond' stamp next to the engine number or possibly in the valley above the loose bores, if so this signifies oversize lifters and bores from the factory.

I will get measurements this week and post them. Will also check on diamond stamp too. It makes me wonder if the lifter bores could have been slightly out since new? I say that because the the other bores are perfect, and the block was standard bore before I got to it.

Engine was running before tear down. It actually ran pretty good! When I bought it the oil had lots of gas in it, from a bad fuel pump. I didn't know how long it had run like that so I thought it better to rebuild. In hindsight, I may have been too hasty in that decision...

You might measure all of em while you're at it

Well, if you're keeping it stck, and keeping the cam smaller, it's probably not a big deal at all. If you start looking at more power and want a faster lift rate (Hughes, Comp XE, Lunati VooDoo, etc) then you may get into trouble without addressing the loose bores. But an older conservative grind (stock or slightly more than stock but an older lobe design) probably won;t cause problems.