bought shortblock from a local shop but something is different

Hello this in my first post here guys. Ill get to the point i need some help figureing out my short block i got from a local engine shop . first off it has been bored decked with flatop pistions but thats not my problem . I just got the motor together and put it in my 87 t-top GT But for got to follow up on the fact that it seems to be slightly different from the other engine i had. the problem is the best i can explain is right behind where the starter is on the block is a threaded bolt hole around a half inch. I have not stared the car yet so i dont know if oil or coolent would come out of it . I am thinking maybe it is a block from a 94/95 and thats maybe a temp probe hole? Should i plug it up or not worrry? I'm only about 5 hours of work from gettting this car running and need to know wtf that hole is lol before i have fluids spraying out.
THANKS GUYS in advance..