Has anyone tried them? I am going to dyno test a factory headed 360 later this year (once things open up again down here), and thought I'd try them.

Have you come up with something that shows an improvement on the flow bench?

No flow testing at all on these heads. I've owned factory small block heads from years ago that had the floor welded up.

I was going to laser cut something like these port plates for Ford Cleveland exhaust ports.

Ford over did the ports on the 351C 4 barrel heads, they needed help on the exhaust flow by closing the up, I will really be surprised if closing up the SB Mopar heads helps them flow better

This thread intrigued me , so I got to looking.
MPG head service still makes those plates , but I could not find any other brand that uses them besides Ford.
Their cam grinding arm , Cam Research showed a flat tappet cam device that breaks in the cam on the bench that had me very interested.
It is done in an oil bath and the spring pressure is ramped up as the process goes on................as they like to say in engineering , " it works on paper ".
60.00 to break in your cam and lifters seems like a bargain in time savings alone , but I suspect that it is brand specific as they only offered the service for Ford cams..

What a great idea...and a bargain, yes it would be great to have this for Mopars!!
YouTube link

Yes the 351C 4bbl heads has int and exh ports bigger than the BB Chevy and the tounge made the Cleveland more suitable on the street. But on a SB Mopar? Arent the int and exh ports appropriately sized for the engines purpose?

I’m skeptical for the same reason you don’t mix used lifters after a disassembly. You also break in a used cam (if you ever re-use a cam) again if installed on a different engine.
There are differences in the blocks that result in slightly different contact patches between lobes and lifter faces.