318 timing chain.....and why the engine should come out.

What NM said
I've done cam doc on 340, comp 268xe. MP 260
The 268xe has the more radical lobes but uses only the chevy portion of the lifter it HAS to have more duration to get the lift it gets
The Mopar Performance 260 uses more of the lobe and is actually more gentle than the comp cam even if it is bigger
the 340 cam has VERY long ramps and is not near as aggressive as the MP cam (which is not at all aggressive compared to todays cams) it is a passenger car cam, warranties and quiet even after high miles and all that)
I'm trying to remember but the 340 cam is a (IMHO) a 280-290 class duration cam
the "260" is at around .008 lift and it gets really long as the tje closes
The Jones 256 or say Howard's or Bullett's 256 versions will outperform any of the above
maybe not rev quite as high but the others are out of breath up there anyway
The Jones is the shortest seat to seat- say at .002- of any of the above and has 50% more duration at .275 than the DC260