Even though, you prime oil pump turning engine over... you have to insure the oil is flowing out of each pushrod @ rocker arm....
Since you have a Gen VI block, what were your lifter bore clearances, if they are excessive when priming engine the oil will dump at lifter bore... If you primed after installing intake, you will never see this. I know; for a FACT the Morel HI REV, better be within clearance specs.... this was a complaint of others, not having their lifters allow oil to flow up to rocker arms, even turning engine over by hand. One reason, oil viscosity was changed, I was able to prime all Hi Revs with pre prime to every rocker arm using 20w50 on two 604 cid, due to the simple fact I bushed lifter bores to bring within clearances...
If you fire the engine and you have some noisy lifters shut it down, let it set. Go back; back off lifter and relash. Sometimes mostly all the time, they will prime on the second fire up. If they have air trapped in piston assy, it will make it harder to prime lifter even running.
The Gen VI 525 blocks are most likely going to be on the bigger side, verses going into a Dart, which will be on the smaller side.

I had Johnson lifters put in my 525's last winter. When we fired it up the first time you could hear one ticking, my builder wasn't to happy. He talked to Johnson and they said to drain the 20 50 oil and put the thinnest oil you can get in there and prime it up. Turned it over a few times and sure as chit that lifter pumped right up. Drained that oil and put 20 50 back in and it's been perfect all summer. I'm no engine builder but just passing this info along so it may help someone down the road.

Not sure if that can't remember now

The thing is , he has ran the engine all summer. This is not a new first start up scenerio.

same scenario.tried to prime engine(fresh motor) could not get one bank to prime.had mercury 20/50.was advised to use thinner oil on first start up then went to 15/40.have had no problem all season.went from morel to Johnson lifters.

Am I sure?, not really... but the springs I used have 189# on the seat. Probably a tad too high. And the lifters I used were Hylift Johnson, not Johnson. Not the same product.

Long story short one of my sets of heads came with solid roller springs 210 seat 720 open the johnson lifters did not collapse I have not idea how but only 2 hours run time that told me good lifters lol

What was open ?

This was also my first season on a fresh top end 525. We left the stock lifters though and used stock spec valve springs. Did a LOT of offshore running this season and not a single issue from the engine. I run 20w50 ZR1 and Wix. I don't buy the higher pressure valve spring theory....

I run HI Rev Morels, i225# open/575... straight 50 weight Brad Penn. No issues.