I have a pontiac 428ci engine in my '79 K5 and can get a GM 400ci complete for $250. I am woundering if I should get the 400 for my '87 K5 or just put the 428 in it. The only problem I have with the pontiac engine is there is a oil leak somewhere and I cannot find it at all. The GM 400 is bone stock but my pontiac engine has a cam, manifold and headers on it already and I am pushing around 350 plus HP and 400lbs torque. What do you guys think would be my best bet on the engine dilmea I am having. Thanks for your help.