The oil passage (to allow for hydraulic lifters) is shown below in the first image. The black arrow shows the lifter bore and the drilled passage is shown by the red arrow. There is a plug for this passageway (shown in the second image) but it is covered by the bell housing so you can't reach around and feel for it (unless your bell housing is removed). This is on the 235. Hope this helps. To see this passage you must remove the side plate (the valve lifter cover), the valve cover, free up one rocker arm (by loosening the locking nut and the adjustment screw), remove that pushrod, lift up the corresponding valve lifter and look inside the lifter bore.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
