We have a recipe for chocolate fudge that is 40+ years old. That recipe calls for a "tall can of evaporated milk" and one (8 oz) jar of marshmallow creme. In the last few years we've been having trouble with the fudge (too thick and hardens too fast), so I wanted to check the ingredients proportions. One problem is that the major brand marshmallow creme jar (western US) is now 7 oz. The other one is figuring out how big the "tall" can actually was. It seems there was such a thing in the more distant past but I don't recall. I did find some comments online indicating it was 14.5 oz. The major brand evaporated milk can here is now 12 oz. So I'd like to find some more concrete conclusion on this. If it was 14.5 oz, then I'm obviously shorting the recipe now. 
From my previous research into can sizes, I suspect that the can may have been either a #1 tall (16 fl.oz) or a #2 tall (24 fl.oz).  There was also a #3 tall, but it’s large enough that I don’t think anyone would have been selling evaporated milk in it. You might want to look at other fudge recipes to determine if either of those amounts might be enough fix the problems you’re having. You might also want to post the rest of the recipe so people can see the proportions to other ingredients. 