I found this in my notes from way back if I wrote it down correct. hyd ball/ball-7.51" (stock 318/360 I'm assuming). adj hyd cup/ball (TA?)-7.23". solid ball/cup (273 I'm assuming) 7.340". Assuming your preload is acceptable from what I gather it is then there is only a problem with the one lifter (or pushrod) & not likely that that one pushrod is way shorter than the rest of em so I'd pull that lifter & open it up and eyeball that lobe to find where all that clearance is coming from then go from there. If ordering correct length pushrods you'd install a pair of rockers & use an adjustable checking pushrod to find the exact length needed to be ordered but I think the problem is confined to that one lifter/pushrod/lobe & that new rockers ain't needed. iirc this is a mild hyd cam