I had a similar problem with my 49. Didn't need to loosen the rocker arms, just backed off the tappet adjustment and was able to slip the rod by.
As far as stuck valves, try tapping medium-gently on the valve stems with a hammer. If any are stuck, you will feel it. The valves that move feel like hammering on a spring, the ones that don't feel like hammering on concrete.

Current fleet (subject to change w/o notice)
\'49 GMC 3/4-Ton , 60 Austin Healey Frog-eye Sprite (some assembly required), 2011 Dodge Avenger, 2015 Jeep Cherokee. No, they don't all run.
My other ride is a (B737)no, (B767)no, A320.... Update... was Embraer E190, now Boeing B787.

Knowledge is a wonderful thing, but ignorance means you don't know you can't do something.