There are steel inserts into the aluminum hub where the sprocket mounts to, so really no need to worry about stripping the aluminum. But, the sprocket mount holes open into the brake drum. They are exposed to all sorts of dirt, brake dust and possibly water. Liberally anti-seize the sprocket mounting bolts or they can seize up big time into the hub. I've encountered several like that, some so bad that the heads were broken off the bolts. The bolts are a fine thread so when they seize up, they do so very badly.
Yes, most of us agree the factory manual is best. You can download free copies of most of them from the XS Cafe. It helps to have more than just the one that covers your year. This sprocket bolt torque is the perfect example. I don't think you'll find it listed in the '75 manual. Many of us prefer to have a paper copy, the actual book. It's much easier to use when working on the bike instead of having to run and look at your computer all the time.
Watch eBay, used, reasonably priced copies pop up all the time. Yamaha didn't publish a full manual for every year, full manuals only came out every 3 or 4 years. The in between years got small 10 to 15 page supplements covering any differences in that model year. They were made to be used along with the previous last full manual. For your '75 model, you'll want to look for the '74-'77 full manual .....
I also suggest getting the '78 full manual and if possible, a version that includes the supplements up to '80 or '81. That will cover all the bases including the change in '80 to electronic ignition and BS34 carbs. Obviously, you don't need that info now, but you never know what the future may bring. An '80s model so cheap you can't pass it up may fall into your lap some day.
