Implementing a PCV system in place of the original draft tube setup into your flathead might be a better use of your resources and prove more beneficial to engine operation than re-engineering a part that is readily available from several vendors. When that old WDT comes out and all the coolant passages are flushed of scaly oxidation and crud, the new WDT needs to fit snugly so its not rattling around in that passage. If the coolant system is properly maintained, then that replacement WDT may not need replacing for decades, if at all...the original WDTs need replacing because poor maintenance has accelerated failure or high mileage has worn the WDT to failure. Even the zinc plated steel replacements appear more robust than the original WDTs as zinc plating has come a long way since these flatheads were manufactured. I did a partial PCV setup and noticed the results right away at the first stop light I idled at...whenever my schedule allows it, I'll plumb the rest of the PCV, which I look forward to as figuring out how to make the PCV system from the original Mopar PCV designs was quite rewarding