I could be wrong, but originally it would have had solid(mechanical) lifters.
I was told to check the bottom of the lifter. If it has bars across, it's likely hydraulic. If it has a C clip, it's solid. However, my lifters looked nothing like either of those descriptions, so it could be hard to tell just by eyeballing it.
If you don't want to physically inspect them from the side plate, you could try this route which I'm quoting from another website:
Hydraulic Lifters have approx. .060 of "squish" in them. . . Solids do not. . .
With the engine off. . .yank a rocker cover off of it. . .. find a rocker that is somewhere in the down position. . . not in the up position.
Loosen it up until the rocker is barely making contact with the valve. Then tighten the rocker nut down, ever-so-slowly. . . . If the pushrod moves down a little (approx. .060) before the valve starts to move, Wa-la. . .. Hydraulic Lifters. .. . .
If the pushrod does "not" move. . . but the valve starts to move. . . Aha !!! Solid Lifters.
