...Also, the reason for the crossover tube as I understand it is not to help oil the tappets on the left side but rather to help the #4 main. #5 is fed from the main passage itself but #4 starves at high rpm and that cross over helps the oil turn and go down to the main bearing. I've done that mod on an engine that had issues with the #4 main showing signs of starvation and it solved it. I have a book from the early 80s that notes that reason in regard to a TA series race engine. All other books after that say it's for tappet oiling.
