I have not (in the over 40 years that I have been playing and racing these motors) seen any 55 motors that did not have the steel line arrangement for feeding the rockers. That being said, I also do not remember just how early the earliest 55 235 I have ever seen is, lol. Could be early 55 motors (with a 54 casting date) could be a leftover 54 stick motor and thus use a different arrangement. The 55 blocks are a little bit of an animal unto their own in that Chevy was still designating specific blocks for stick motors and a different block for powerglide equipped motors in the passenger car line with stick motor blocks not drilled for hydraulic lifter use. My understanding is that 235 truck motors did not ever get a powerglide, only a stick trans, thus, solid lifters only. What this means is that you can retro fit a 55 powerglide passenger car block with solid lifters, but you cannot retro fit a 55 stick block with hydraulic lifters. This changed in 56 for the passenger cars in that all 235 motors from 56 forward came with hydraulic lifters. Now I don't know about the truck motors from 56 forward as I do not have any in my stash of motors so I cannot say whether the truck motors continued using block not drilled for hydraulic lifters (would love to know the answer to that though). Same for the rocker oiling. I cant imagine that the 56-58 truck motors did not use the steel line arrangement. I can say that 59 and up 261 blocks did not, they used the same upgraded direct from the main oiling as the 59-62 passenger car blocks.
Hotrod Lincoln, the oil filter is not exactly gravity drain into the pan. You are right though, it is to a degree. The input is pressurized from the oil sending unit port, albeit, a bleed off of the pressure. So there is some gravity drainback in that configuration just because of the way the filter hangs. When you run it to the side of the head for the rockers, that condition is eliminated, it is pressure in, pressure out. I have had one of Charlie Baker's bootleg offy sideplates on various of my 55-58 motors for many many years now. The side plate did not fit with the 55-58 steel line installed. I removed the line (installing plugs at either end of each boss) and ran the oil output to the side of the head and fed the rockers clean pressurized oil, just enough to allow the rockers to dribble. I raced and beat that motor, and others in the same configuration, for years (just recently removed one that I built that way in 1985 as a running motor to put a very modified 261 in and the rockers on that motor look as nice as the day I installed them all thouse years ago. Again, though, you always have to double check the work and make sure all of the rockers are getting sufficient dribble pressure, especially No. 1 and 6 cylinders and that the stock style canister seals can handle the pressure. It’s been hit and miss with me although I switched to a remote spin on using small lines a number of years ago (I am not currently running any filter on the 261 bypass style motor).
Also, you might have noticed that the 55-58 rocker connectors have an open loop, while the 59-62 and closed up. The 55-58 loop is open because the engineers expected excess pressure and volume to bleed off through the loop. Unfortunately, when the motors got old, a restriction was sometimes needed to keep sufficient oil to the rockers. Many many mechanics pinched off the open loop in an attempt to gain a little more pressure and flow with an older engine. I do the same.
