While in the Air Force we got GAF on occasion, I recall that it somewhat more grainy than Kodak Plus X, but had nice tone, it was rated at 100, so I would start at ISO 50 and work down, my choice of developer would be HC 110, less fog, a good developer for out of date films. Although frozen expect some fog, you can add restrainer. Or if you have any luck on Ebay and find a bottle of FG7, clean working, good sharpness, and like HC 110 low fog. My NOIC alway wanted to match film and a developer from the same company, for GAF we could GAF 17 or was it 14, their version of D 76, softer working.