I’m rebuilding my first Flathead and I have some questions

[50MercMetalHead]

Hello! (First off I wanna give a disclaimer: I’m 22 and while I’m not necessarily new to engines or even all that new to Flatheads, this is my first full rebuild of any engine and I still have a lot of learning to do.) So, I’m rebuilding the 8CM out of my 50 Merc, it’s bored .040 over from a previous rebuild, it has the mercury crank (unfortunately no matching numbers to my car though). It ran perfectly before I pulled it, except it was losing oil pressure, only making about 5psi at slow idle, but about 15-20 at fast idle, so I pulled it, and found a considerable amount of sand in the engine, I believe it’s casting sand but anybody’s guess is as good as mine. Bearings are all junk, but the cam, crank, valves, lifters, and cylinders all look really good, I assume the last rebuild didn’t have many miles, it was just done decades ago then sat for most of the time. So I’m basically going to reuse most of the internals.

I’ve managed to get down to just the block and I’m about ready to send it off to the machine shop to get acid dipped and to have new cam bearings installed, the only removable thing left is the crank breather/road draft tube that runs from the crankcase to the intake via the lifter valley. Im not really able to get the tube out without wrecking it, and it was already really misshapen from whoever rebuilt it last, so does anybody have a source for finding a replacement? I know it’s just a plain old 1-5/16” tube from other posts here, but I haven’t had much luck looking for a replacement.

Another thing that I’m wondering about is the cam/lifters in flatheads, I noticed before I tore down very far, when the valves were closed, the lifters and cam heel would lose contact with each other. To me it looked intentional, because they all did it, but my dad (who has no Flathead experience but plenty of OHV experience) said that seemed odd to him. So I figure I should make sure they’re supposed to be like that, but I didn’t see much information about it in my searches.

Also, I wonder about my oil pump. It spins nice, and looking at the rod and cam bearings I see they’re more than likely the cause of my low pressure, but I’m worried about putting this pump back in as is. I’m really stuck on the fence about whether I should reuse, rebuild, or replace. I’ve heard the issue with Melling pumps and I’m worried about going that route, has that issue gotten resolved at all? If this pump turns nice should I just clean and run it? Is there an easy way to bench test it that I may be overlooking?

I think that’s all that I was wondering for now, I’m sure I’ll think of more in the future though. Thanks in advance for any input or for simply just taking the time to read this.