How far ?

[IMNCARN82]

I'm looking into re-building this 340. If I have a valve job done,should I replace the piston rings?   

[Chryco Psycho]

I guess it depends on how old the engine is but generally yes replace them , you do have to at least hone the cylinders to get the correct finish in the bores though so the rings will seat in

[IMNCARN82]

Thanks CP ,that's what I figured.  This engine probably has 50K on it. The reason I consider the valve job is there's alot of carbon build up in the exhaust ports on the heads.Alot.  She would smoke some on start up,only sometimes.Probably valve seals?  When I replace the lifters do I have to change out the cam?   Do I just re-build the whole engine?

[Chryco Psycho]

Carbon could be intake leak , valve seals / guides or just fuel
You can use new lifers on an old Cam If you like the cam although more modern grinds may be a benefit , what is in there now 
Rebuilding the whole engine definatly makes sense , it is a lot more work to redo it again later , this doen`t mean every parts need to be replacd but it should be clean & checked before reusing any part