Just make sure you get one from 1990 and back..91 and up is different.how do you know it's wrong? if it's just a matter of what it reads, then make your own "full" mark with a chisel after you change the oil next time..
the stick and tube should still be available from GM for not too much money... it's going to be for a 454 truck application and might not look "correct" if you are into the numbers matching thing, but it will fit and it will read correctly...