Cylinder #7 down on compression

I drove the car all season and it felt like power was down some. Not sure where this winter project is going to go but today I was off and decided to do a compression check. Engine cold and all plugs out 7 of the 8 cylinders were low of 137 and high of 155.......Cylinder 7 was at about 110PSI.......Not good at all.......engine is 70 340 matching number to my Duster. I am not burning oil so I am thinking valve issue. Checked springs on #7 and pushrods and they look good. Where do you recommend I go next? Should I pull the intake and look for cam/lifter issue? Can a leak test be done with heads still on engine in car? No idea how to do a leak down test but I willing to give it a shot.