I saw this was related to Gurths symmetrical placement!
The only conclusion I can make is that R4C6,R5C5,R6C4 must be odd!
Then it unfolds with a skyscraper and a naked quad!
So these are the only valid placements of Odd and Even candidates on the Diagonal!
So R8C2 =1 and R2C8=3!
Quad 1579 box 3!
Quad 3579 box 7!