am not sure 100% sure of the difference for these. Is it solely the color of the overprint?

Scott 16/17 (SG 12/14) are black and the Scott 26/31 (SG 33/39) are listed as shiny blue black. The recommendation is to view backlit with 50x magnification - easier said than done.

For the 2 pence, I want to confirm if this is Die I or II.

If you count the line crossing the top of the head, it would be 3 4 line (Die I) and if inner frame is closer to design it would be Die I.

BTW, I see variations of color of the overprint and see bluish tinges but no experience to know what I am seeing.