The 440-3 and 413-3 were designed for extra heavy duty cooling purposes as many were used running continuously under load for marine, water and oil pumps, and generator applications. Both had anemic compression ratios down at a measured 7 to 1 or less.

413 uses a skirted themrostat as well, and as you noted will run hot with the regular non skirted variety- no matter what the little guy at autozone and his computer tell you. The 413 variety is radically different with a high mounted water pump housing that bolts directly to the heads, and the
heads have closed chambers that measure about 90cc and use sodium filled exhaust valves. Both the 440-3 and 413-3 heads have the peanut plugs located in the center of the chamber like a small block Chrysler. This helps alleviate detonation, along with the extra plug cooling passages.

I am working on a frankenmotor 440 rv block with the 413 small valve heads. Between the heads getting cooling first due to water pump design, the quench I will have with a zero deck piston and the closed chamber, and the cooling effect of the sodium exhaust valves, I should be able to run 9 to 1 compression on 87 octane swill. Motor will be all done at 4500 rpm which is fine for my motorhome or any towing application. Plan to run a 518 overdrive as well to keep the revs down with a 4.56 gear and 32 inch tall tire.

For those working with these that want a nice stump pulling torque cam for towing or RV get in touch with Mike Jones he will fix you up with his special grind for these engines. Sligthly higher duration with way more lift and area under the curve.