all depends on build I have bushed lifter bores and was told a crossover tube was a waste of time I did enlarge all oil passages to and from pump and main bearings and restricted oil to cam bearings since I run external oil lines to rockers.

70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake

best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4