I have bought a lot of planks (not blanks) of maple from sawmills and used to specify 10/4 thickness by 8" wide. 60" will cut out one blank plus lots left over for handles, pistols, etc., and a regular 8' length would easily make two long stock blanks. If you want to make an Ambrose Lawing or a Bedford County rifle, or similar looong drop profile, get a 10" wide plank.
If it's any help to you or your friend, I came to the conclusion that this is generally a lousy way to buy stock woods. I got tired of lousy quality wood ("super premium curl" my foot...) and musket grain through the wrist. It's certainly possible to get great stuff if it's a small mill and they'll let you crawl all over the operation and dictate what you want and how you want it. Good luck trying this with anything like a large mill. You'll take an old cold tater and wait and when you see Freddie's or Wayne's stocks at a show you'll drool all over the great stump cuts they have.