As far as action work on a savage... if you want to true up the face, go ahead, I wouldn't mess with the threads, the floating bolt head design should take care of any misalignment there.
The different actions- SF and CF, refer to the bolt spacing of the action. In short actions... The SF (Staggered Feed) measure about 4.250 from action screw to action screw. The CF (Center Feed) measure about 4.400. These are both generally blind magazine rifles but can be had with detachable or hinged floor plates. Another way to tell is if it is a blind mag, when you pull the action out of the stock, if the mag box stays on the action it is a SF and if it stays in the stock it is a CF.. In long actions the spacing is the same (5 +inches) but the blind magazines follow the previous rule. The actions of all the models are pretty much the same except for the target and LRPV models. The 10, 11, 12, 14, 16 are all short actions, and the 110, 111, 112 etc.. are long actions. The 16 series will be Stainless, and some of the 12's are as well. Many of the other letters etc. determine the "package" of the rifle, as in comes with accutrigger, factory scope, synthetic, wood, or laminate, etc, etc...
I'm not really sure I follow on what you are trying to say in the first couple sentences. I would recommend using the barrel nut as it is super easy to set headspace that way if you are doing this yourself. Spend the $12 on a barrel nut and save yourself the headache, but that is my opinion. I bet your son could care less and would be just as happy to be out there with you.
These savages are cheap (relatively) and would make a great rifle to teach a young one on. You can always change the barrels yourself as they grow up and can handle more recoil, etc..
--And, if this is an older pre 1996 "ish" action.. Let us know, because they did even funnier things back then.