Help translating an older Recipe
"Sweet milk" is indeed standard fresh milk. It is just how people used to talk about it, to distinguish it from "sour milk". 

"Sour milk" is also "buttermilk". It seems that over the years, people stopped selling actual buttermilk (which is the whey left after removing the fat from the sour milk) and started using the name "buttermilk" for what used to be known as "sour milk". 

If you can't find graham flour, whole flour of mid-coarse grind will be a good approximation. 

Baking soda and baking powder are good guesses. You could go with the original amounts, but if the first batch comes out overleavened, try reducing it. In the decades since the recipe, producers have found out how to make baking powder which does not go stale too quickly, does not lose much of its action on touching the liquid, and so on. So maybe the amounts are better suited to weaker leavening. No way to know without trying. 

The cans are not a good idea. I don't know about cans then, but the new ones could be lined with plastic (which will melt), or be rusty. The recipe is very obviously a cheap recipe from times of limitations, maybe Depression or WWII. Just use a baking pan. If you are afraid of bad leavening, using a wide one or two small ones is better than a single deep one. 

Also, don't trust the "one hour" suggestion, not only because you're changing pans and because the ingredients might have changed in subtle ways over the years, but also because baking by time is always unreliable. Test them for doneness with a thermometer, or in the worst case with a toothpick.