Most of the water in the oil problems with big blocks I've found are in the heads (cracking by and between the valves),but you can take that 402 .125 over standard bore.The 396 is the only big block you can't go more than .60 over safely because of the casting flaw,the 402 is a .30 over recast of the 396. I dont recommend going that far over because of cooling probs and the pistons are pricey, If you could find a 454 block,you could use your crank and rods, buy some pistons and build a 427.That way you increse your cubic inches but keep your rotating mass lighter. Not to mention you can buzz the he!! out of them.Good luck
