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.