>After replacing the seals on both ends of the tubes, I passed them through
>the rocker box, and into the holes in the engine block. The problem is, 
>even with the head torqued down properly, they are not really tight into the
>engine. I can pop them out without too much effort.
               ^^^^^^^^^^^^ Oh Oh!

yes, you can replace them without removing the heads (just the rocker arms), 
finally!

        Are they the right length? You need the specs from Bentley. When 
they get old and rusty the accordian pleats at each end collapse. You can 
pull them back to length easily, just slip them over a wooden dowl and pull 
out evenly with your hands. If they are very rusty, the pleats will crack, 
and leak oil despite the seals fitting snugly BTW. Replace what you can 
afford to if this is the case.         Scrape and clean the bores that the 
O-rings slide against using a plastic/hardwood stick. This lets the seals 
move with push rod tube thermal expansion and still seal against the 
heads/block. DO NOT use silicone sealer goop!

 tim s.