WOW, interesting problem. Could be several things. FIRST, look at the dipstick. Does it say FULL? Assuming the dipstick is correct for the engine and someone added a 2" section to the sump, there is more oil in the pan. SECOND, drain the oil and refill it with 6 quarts. What does your dipstick say now? IF some bozo extended the sump and did not lower the pickup the same amount, the pickup is way up there.....normally, the oil pump pickup is really close to the bottom of the pan.....if not close to the bottom, it can be picking up foamy oil....and lower your oil pressure. IN ANY INSTANCE, you probably have to pull the pan to figure out what the problem is OR to change the oil pump. High Volume pump wont hurt, dont do a High PRESSURE pump. Do a search on Google regarding how to measure the distance the oil pickup tube is off the pan bottom....easy to do. Probably smart to replace the pan with a stock pan. There are different pans for a small block chevy.....right hand dipstick vs left hand. Also, the front curve radius has two different configurations.