Sounds like stuck seals.  Probably carbon gum-up or minor rust.
What vendors apex seals and springs are these?
Home Depot Zep Industrial purple is a great degreaser.  Acetone is another common remedy.  You may be able to spray or brush it into the apex slots.
If you have access through the exhaust ports, some forced mechanical movement in every direction by tape covered needle nosed pliers may help restore movement and possibly remove surface rust.
Some folks out there have poured acetone through the spark plug holes to get an old (sometimes seized) engine running again.  I've heard of more than a few people complaining about coolant/oil seals later...
Do you recall the apex clearance assuming you rebuilt the engine?  You might be able to check apex clearance in place with feeler gauges while you are at it.

Cheers
Cary