Can Win 748 be used for the M1?
It would appear so...
I have a Hornady 7th edition, (2007) and it does have a separate section for the M1 rifle (.30-06), and Win 748 is listed in it, for two of the 3 bullet weights given.
Interestingly, Win 748 is NOT listed in that manual in the regular .30-06 data. Nowhere at all.
Win 760 is listed.
Listing a powder in your load data means it can be used. The opposite in not true. Not listing a powder just means they chose not to list it.
Not listing a powder in your test data can be for several reasons, most common are, the powder was not suitable, or they did not achieve satisfactory results, or they didn't have any to test, or most often they simply, or didn't bother to test it.
Generally speaking, the data in the books is what the testers believe most people want. They cannot test every possible combination, and generally focus on what yields the most commonly sought results.
For example, you generally don't find reduced level loads for magnums in the books. its not that they don't exist, its that most people who shoot a magnum are interested more in magnum level performance, and the data is tailored to reflect that.