1995 chevy lumina engine replacement?

i have a 1995 chevy lumina 3.1L engine...a couple months ago i had a bottom end knock and the engine just jammed up. so now i have to get a new engine but when i look for a 3.1L it has options such as "upper, ctr AC mtg on block drilled/tapped " and "upper, ctr AC mtg on block not drilled/tapped " im not too sure which one i have and mechanics cant tell me over the phone so is there anyway i can check which one it is? maybe pics or links? thanks