Hi I'm new... got some valvetrain issues

[YodaRoddin]

Ok, so ive got a A Body with a Mild 454... I first thought I had a collapsed lifter. The noise started out being really intermittent... and with a couple rides, its become more constant. ive checked the rockers, and marked the pushrods... all of them turn, tho some were turning real fast (I bought the car running) so I tightened those up just a tad so they turned like the rest. None of the roller rockers have loosened up afterwords, so I don't believe it's eaten the cam yet. I tried pushing down on the lifter side of the rockers, but oddly none of the lifters give that "spongy" feel which would indicate the bad lifter. When the noise does occur, there is definite power loss (Skipping) telling me an intake lifter isnt opening very well. heres a clip of exactly how it sounds....

http://www.youtube.com/watch?v=pVA4eedOYTQ

so now my plan is to remove the manifold and see if any of the lifters are ground on the bottom, at which point ide be able to install new lifters and be on my way should their be no abnormal wear on the contact surface oflifters..... now if the cam ends up being shot I have a Comp Hi Energy 268 Kickin around Ill put in (I think its a 260 now, quits at 5K)

So aside from any helpful info anyone has heres my question... this 268 cam has been grooved for a 66 Block. Will I have any problem with running this in a Later Block that doesnt require this groove?

Any info Greatly appreciatted!

EDIT: Also, my oil pressure hasnt changed at all. it hovers below 60 cold, around 45 warm.