The only one that seems to care is you. Go help out the guy with his 454 cam decision and don't stink up this thread.
According to all my farmer friends 454's are very seldom used for irrigation pumps for durability reasons, something to do with a horrible rod ratio. Most use and prefer the 370 Ford industrial. Iv'e heard they have a few running now pumping out the Salton sea for land reclamation.
Yes they had shaft rockers except for the ones that didn't have rockers at all. Y block Fords sometimes got plugged oil passages. Never heard of it on GMC/Chevy 6 cylinder engines. Or Studebaker engines. Or all those millions of pre 1949engines that were built with solid lifters. Never saw a stud mounted rocker till 55. Lots of things happened before you got involved.
Call Denny Wydendorf and he'll walk you through it. Here's his kit and reamers. http://wydendorfmachine.com/reamerkits.html 460 has a similar oiling passage to the 351C; neither have priority oiling to the mains. Bushing the lifter holes (with bushings that have a small oiling hole) will send more oil to the mains instead of putting it in the valve covers.
What is the cut off? Hamb drags pre 65. I posted a El Camino That had a 65 GTO front clip and other panels to make it look like a Pontiac truck and it was pulled but a late 65 rat motor is OK.
The blocks i have seen bushed on 1 side had a 0.030 oil feed hole drilled to feed a solid roller setup. Are the bushings honed to size because most would drill first.