Update:
The OP has since identified two of the unknown WIF characters at the end.

Is the paper missing after Kw or is there enough paper for some letters, so that the chemical analysis would help you to recover some more characters to make the calculation easier?

For example:
Kw**********jcQ...

** -> paper / chemical analysis / recover characters
****** -> hole / no paper

-> so you would have 6 missing characters