Ouch.....
I had outstanding luck with Jesel spotsman series stuff on my W5 motor, ran them for years, and the new owner still does. They hit 8k a number of times by mistake..lol..and never an issue.Sweet bulletproof stuff.

So.....I decided to call Jesel, and find out what if anything they offer for a standard style head, turns out they have an offering.
Its part number KPS 09749 these require milling the stands to fit( an operation they offer for 100 bucks a head, you send the heads, they set them up.
These arent the sportsmen series, they are pro series, and are 1600 bucks a set complete..Will handle 800 spring pressure, and clear a 1.600 spring( larger than would even be required) with no clearancing.

Not cheap, but at least an alternative i wasnt aware existed.

69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, low 10.30’s 1/4
1.41 best 60 foot
6.56 at 104.17