Let it sit overnight. Then next day GENTLY tap the pushrod end of the rocker arm with a hammer. If it gives it's hydraulic. If it doesn't, then most likely it's a solid lifter.

This isn't foolproof, but works in most cases.

Letting it sit drains the oil down and "relaxes" the valve train. Don't start the engine until AFTER you've done this or you'll put everything under pressure again.

Good luck