Actually those (Moroso maybe) inline AN filters where design for that application
I ended up breaking two oil pump drives on that deal before removing the pump and taking it apart One was a new Hi Po Mopar brand and the other was good use stock one, they both snap, twisted off, around the exact same place on the tips
I had to borrow the third one to run that race, I replace it later in that year at another division race

too bawlzy for me. Them engines can barley oil themselves in a perfect world, when you start to get past 6900-7000.

Im with B1MAX... these motors (B/RB/Hemi) have been raced for over 50 years with little to no modification to the external oiling set up but for some reason this one is special????? I think there is an issue that a check valve will not help. But thats my 40 yrs experience talking so I may be wrong
As a point of consideration...every fitting.connection will cause a disturbance in flow (reduced flow) and most if not all of us that have had check valves in any type of system have never seen them fail....as an example I had a check in the oil cooler line on my Bruno, it (the Bruno) got hot enough to melt the DOT spec vent hose laying on the case, why because a piece of debris got in the check and wouldn't let it open (the pressure side) want to bet whats going to happen on the suction side???

The reason I’m not using a filter on my 340, pump feeds straight up to galleys not through all those 90* bends and through a filter that restricts flow. If your pump stops working (0 pressure) let’s see you kill the engine before it blows. By the time it drops it’s already over and gone. Filters are for street cars.

Seems the least harm here can come from a check valve on the pressure side, not the vacuum side. Oil CANNOT leave the immersed suction side unless somehow air to replace the leaking oil can somehow gain entry, and a pressure side check would "check" both air and oil, regardless of loops, fittings, etc.
How/where you can place a check valve on the pressure side for a BBM is above my pay grade.

The closer the oil is to the pump ,the quicker it will prime. I had this problem using a Milodon aluminum pump with internal pick up. The pump needed a bigger O ring on the snout/drive end of the pump. It will suck air if that orific is not sealed.

Short line mock up.
While I am concerned about the check valve restriction, I have to keep reminding myself that on my “race” motor that I spin 7500 it uses a 3/8 internal pickup and the bearings always look good on it when i take it down. Even with the restrictions on a 12AN line it seems it has to be getting more oil than the internal 3/8 pickup. I was first concerned about the 120 degree fitting at the oil pump being a restriction but it does hold 80lbs at idle.

I like to think I'm familiar with every Milodon Mopar oil pump of the last 50 years but I've never seen one like that.

Me too, maybe

It is what you get when order a 21815 (the photo is old to new design)-it just has a Meiling pump cover on it. I called Milodon and they had no reservations with me using the stock style cover on it. It is the same with the their pump cover with the OEM style pump, I think they are designed to be used with OEM parts.

As has been mentioned, the one-way valve might be restrictive!!!

Guess you haven't looked in a Milodon catalog in the past ten years ... these aren't new !!

FWIW, now that I see the pump open I recall drain back issues being related to the design of Milodon's rotor design. If you were using a standard HV pump with a Milodon block plate for external pickup you would have no issues with drain back.

Interesting on what you say there, I have one of each type vanes and debating which would be better.

The rotor/vane issue goes so far back most are too old to remember it. But the issue is real.

Use one of the Peterson primer remote filter mounts. Spin it with a cordless till you have pressure and go. I would check both fitting hose joints on the suction side. If you're loosing prime you have an air leak period.

I don't like external filters but those things are so sexy.

Now if we could only get Peterson to incorporate a pre-screen, we would be all set.

Here's what I've run on my hemi for many years w/ no issues at all. Milodon pump w/ a stock cast iron pump cover. 7200+ rpm.

I've always used a 180 degree fitting on the top and never ever had a no prime issue.Now before I started using a 180 on the top nothing but problems.The 180 has to go over the top of the oil pump and against the block for it to work.

Who popped a wheelie and bashed his oil pan on the return to earth
I'm glad it didn't tear it open