[TR] compression differance

[Gary Nafziger]

Just a question here for some thoughts from people with more experience. 
While in the shop getting tuned for the driving season after an overhaul my
mechanic measured the compression on each cylinder (tr-6).  He found two
cylinders with 20lbs differance from the others.  This is a newly overhauled
engine which I assembled.......(which might be the problem? LOL) 
anyway.........i've only got around 300 miles on the engine.  Could it be that
the engine needs more time and miles to get the pistons/ rings to seat?  Or is
it valves?  or is it more? lol

thanks in advance!

gary n.