Restriction plate between the thermostat housing and the head?

I cracked a head recently and my DD expert has never seen anything like this before. Is this normal? Do we need it or should it be removed?

It's the second cracked head I've had on this engine.

750hp. I can't tell if the other has it without pulling things apart. It wouldn't be on the DD parts list. My DD expert buddy was a DD mechanic and ran service for Harper Detroit up here for years. He's spoken with other old experts and nobody ever heard of them used. Our plan is to keep them but remove them.

2 cracks on this one, between the valves.
I believe it's a heat issue - but I'm certain it never exceeded 200 on the gauges. I've got a murphy gauge on that engine, so when I check that it was even lower (I've never seen that hit 180 - but that doesn't mean it doesn't, it just means that by the time I run down there, it's not).
Last year I replaced the inboard (port side head) with a new one. The one I've got to replace the other is new also. They were moving parts from the old head to the new one when they saw this restrictor and can't figure out why it's there.

both heads, 1 last year, 1 this year? If that's the reason, I'm good with it, just don't want to ignore a potential bigger issues.

8v92

Thanks! so I should leave the restrictor plates in there?

I don't have EGT - but I'll put it in when we replace the head!