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Well, I am wondering if the different passages, or lack thereof, on the new powerhead will affect the way that 1968 drain system was supposed to work. It maybe that the passages/check valves are not longer there on the new powerhead leaving the old drain system inoperative. I would have to have a very close look at the new powerhead to see if it would work properly. I’m guessing that an actual replacement powerhead for this older model would have detailed instructions on how to adapt/deal with the drain/recirculation system…
Frank is so right, that new recirc system was poorly thought out and made the engines idle like crap. One rich cylinder, the other one is lean. So, trying to “dial in” the low speed needle for smoothness usually resulted in a lean spit. Usually, you had to leave the engine a bit rich to avoid the sneezing, which lead to plug fouling, especially on low tension models. Just seems like that single recirc hose should have been split and delivered equally to both bypass covers….