oil pump/pressure gauge

just got a 88 C/K 2500 4x4, 350 engine(not original) not sure whats up with it, with the truck off it shows 30psi, as soon as i put the key in the on position, it goes to 60 and stays there, any ideas?? would it be easier to get an aftermarket gauge?? also, when i accelerate, there is a tapping sound, like a lifter or rockerarm, only does it when truck is cold or, as i said, accelerating, once in a long while it will do it when i'm cruising, oil pump maybe? and do ya have to take the timing chain cover off to take off the oil pan on a 350? i know ya do on older 318's.

sorry guys(and gals), my first chevy, dont know much about em, so bear with me, you'll prolly be seeing a lot of questions from me, lol

thanks for any help you can give me

actually on a 350 you have to drop the oil pan a bit to remove the timing cover so you woule be good there, but I would start with a pressure sending unit, or put in a manual gauge like you said and see what kind of oil pressure you have