I have an 87 Trans Am. I recently bought a 350 block with cast iron heads casting number on the heads are 3998993 the question i have is how do i find out if the lifter retaining bolts are screw in or pressed as i have recently broken one off there is no nut below the lifter so i am thinking they are pressed in. any help on this matter would be apreciated.

Lifter retaining bolt? I think you mean the rocker stud. Lifters are down in the valley, sitting on the camshaft.

993 heads will have press in studs unless someone has spent the money to have the stud boss machined off and tapped to use screw in studs.

A common fix for a pulled out stud is a screw in replacement. The stud hole is drilled and tapped and a simple screw in replacement stud is screwed in. This is a factory style non performance replacement.