Edelbrock Heads for 318

Mopar crates are not dyno tested or run. They are spun to test for oil pressure, and in some/many cases, they ignored what the reading was. The MP 408 uses stock rods, and hypereutectic pistons too. IMO, neitehr of those belong in an engine that uses a 4" stroke. Not because they are junk. I recommend thier use and use them myself all the time. But because everything has a design limit, and with a 4" crank, those pistons are at their limit by 63-6500 rpm, and the rods slightly higher with the lighter weight of the pistons. The hyper piston requires stock LA rods to be narowed at the pin end to fit the piston. So they run Magnum rods. You never see factory rods or hyper pistons in kits for sale. Well, almost never. That's because the good builders dont want to build to the limit. They want to build beyond the limit just in case. Cheap is just that.

Now, back to your 318 build..A 318 witht eh 360's 3.58 stroke crank is a 349. But it's not a 318 anymore. 400hp is easy to get form a 318/321...But you need to realize it will be at a higher rpm point than a 349, or a 360 if built identical. The reason the 390 idea is around is because the same crank and rods that are used in 416 (340 based) engines will drop in a 318 block with no more mods than the rod clearancing. So a custom piston and you're done. The magic is in the crank. That longer lever gets you more power where a street car needs it. So build whatever you like. I dont like crate engines, but that's me.