u/CoveredInBeeeeeeees

I bought a circa 1976 kit from eBay and the fabric is quite yellowed and has some dark marks from where the fabric was folded. It also has some staining from the masking tape that held it together in the package. I am most worried about the marks that would be visible once this is framed.

Any suggestions on how to clean this? Most of my internet research related to cleaning completed pieces.

Any help is appreciated!