408 Magnum stroker running hot.

I have a 22” champion 4 core on my 416” stroker. No cooling issues.

I think they cram the cores in. I would bet the 3 core would be fine for me too.

People have always had good luck with the HHR OEM fan.

I like that you have factory pulleys and ratios.

IMHO, you’ve got too much compression and too much timing for pump gas. Not sure sure retarding timing is going to overcome it.

Try some 100 octane or more and see what happens.

Seems like a ignition and/or fuel issue.