mecahnical or electric pump? also need to know how much mileage, what year, what carb do you have on it? if its a stock fomoco carb thats instant replace it sign right there.... borrow or rent a fuel pressure gauge, check fuel pressure to find out what the output is... should be about 5-7lbs, also check for volume coming out. btw a 390 is not a small block its an FE series which are considered a big block