If the valves are adjusted fairly loose, you can probably get a good compression check. If they aren't, you may get low readings. Here's the hydraulic setting procedure I posted earlier, once again.
"You can do that as the manual states, carefully and one cylinder at a time, setting each cylinder at the top of it's compression stroke, loosening the adjusters for that cylinder's valves, feeling the push rods for side play, and tightening back to remove the side play. When tightened back to the point where the play is just gone, that is the point of zero lash. Although the service manual says tighten an additional 1-1/2 turns, that assumes the lifter internal piston is free to move, and is at the top of its travel. There was a late '50's Chevy instruction that suggested only tightening 3/4 turn from point of "felt" zero lash. You may wish to try that - after you confirm that you have hydraulic lifters."
This follows the factory manual. I do suggest only tightening 1/2 to 3/4 turn from first point of zero lash. Run the engine for a bit, then reset. Jerry posted a very similar set of instructions on adjusting hydraulic lifters, which you may find more succinct than mine.
Hope this helps.
