I had the 4-barrel power pak soaking in Evapo-rust for 6 days as it was filthy and rusty, the Power Pak manifold is from a 1958 Plymouth 318 Poly i think! part number is 1828103 a friend got it with a 58 Plymouth he imported into Australia a long time ago, and he gave it to me back in 2019. I called it the mystery manifold because i did not know what year it was from and after watching a TH-cam video on a 1958 Plymouth Suburban wagon where the owner took off the factory 4-barrel manifold on a seized engine and the part number was clearly visible so i was able to deduce that my manifold is also from 1958, in 1957 and 1958 Plymouth called the 4-barrel a "POWER PAK" and the 2x4 barrel was called a "V-800 SUPER-PAK". There are other 4-barrel Poly manifolds with different part numbers from different years also anyway I am using it due to having some fitting issues with the Edelbrock tri-carb set up. The rust remover sure stripped off most of the surface rust but due to how filthy the manifold was i will soak it again in fresh rust remover again before i paint the manifold, i am taking a leap of faith and assuming that by changing the heads back to 313 heads that the water in the oil issue will have been solved because if that has not worked i will not be impressed and will then remove the 313 and use a different poly.