My '67 and earlier Sideoilers are not drilled for hydraulic lifters. There are no plugs that can be pulled or changed that would make it work in any shape, form, or fashion with hydraulics. The block would have to be drilled from end to end and through both banks of lifter galleries to make it hydraulic lifter capable.
Because I favor solid lifter cams anyhow, I block the two
oil galleries for the
oil going to the lifters in hydraulic lifter blocks just to increase the
oil flow to the other needed areas. I also check that the upper angled oil gallery at the front of the block does not intersect the hydraulic lifter bank on the passenger side of the block as it may have to be blocked here also. If you overlook this one, then oil is still feeding the passenger side lifter bank regardless of blocking off both galleries at the back of the block. Blocking the lifter oil galleries has been the difference between needing a high volume pump versus a stock volume one depending upon the bearing clearances.
My Shelby block was another story. The Shelby design for the oil galleries has been changed such that the lifter oil galleries cannot be blocked without stopping the supply of oil to the topend (rockers). I'm using Crane roller lifters that were supplied for my Fe that are also apparently designed to use with Ford engines supplying oil to the topend through the pushrods (SBF, 385 series). Normally this would not be a problem for a block that was not supplying oil to the lifters but on the Shelby block I ran into a problem; too much oil pressure was being bled from the lifters. Seeing as how I couldn't block the oil galleries, I modiified the lifters so that oil could not pass through them. Problem fixed!