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Do you have any idea what the backing plate is used for?
I don't know. I've a suspicion that some engines had two holes in the cleaner head matching to two holes in the engine block both carrying oli to the gallery (or direct to a main bearing). Other engines didn't have the extra hole in the block and may have had a return line the sump nearby. Thus, the plate plus two appropriate gaskets allows the two hole cleaner head to be used with the one hole block.
I'm baffled by the variety of gasket arrangements that have been used over the years. Basically, the cleaner body has one inlet from the oil pump and two routes out, one goes to the oil gallery (possibly via two holes). and on around the engine. The second way out takes excess oil back to the sump. This can go via the engine block (where the gasket has three holes) or via an external tube to the sump (and the gasket has two holes). In addition, over the years the number of bolts going into the block changed.
I recently completed a few updates and fixes. The oil filter pointed downward, no oil in the filter at startup. This caused the oil pressure to delay at startup. I replaced the oil filter assembly with an up facing filter, proper oil pressure at startup. The sump was damaged and leaked lots of oil. I replaced it with one in excellent condition, with no oil leaks. I added a fan shroud too. I used a small kerosene flask as an overflow tank. It's been a while since I worked with copper, so it's got a custom copper catch can now.
There are still a couple of minor oil leaks, one's the intake cams oil feed inlet. Someone had damaged the banjo bolt threads, so I had to install a heli-coil insert. I tried new copper washers and crush washers; it still leaks a little. It might damage threads if I tried to tighten it more. It recently started leaking a lot of oil from the rear transmission seal. The seal was replaced during the rebuild. I have another new one on order. The yoke may have a groove in it where the seal sets.
The current transmission is a 4 speed with a Laycock overdrive unit. Is the main cast iron gear housing the same as manuals without the overdrive? Is it possible to replace the overdrive unit with a standard output shaft and tail housing? If so, what years of output shaft and tail housing would be a possible replacement?
