Don't mean to be That Guy, but I'm a little confused by the OP.
Unless things have changed a great deal, Project Appleseed teaches Americans to be as effective as possible with their rifles
, whether or not they conform to an ideal training rifle. That means trying to get the best out of whatever carry strap they happen to show up with, rigging a temporary sling for them if they choose to accept our help, or going without if they decline.
I have shouted from the mountaintops that M1 GI Sling is Best Sling to any who will listen. Before we put a stop to it I sold dozens of them at our events. I have ten of them in my own safe, one is even on a shotgun. But I'm not going to turn away or even criticize someone without, whether he just has to have a Magpul Shadow Stalker Costa Assault v87 on a one-point mount, or he rolls up with a Mosin that hasn't seen daylight since the Tsars. If you showed up, I'm glad to see you.
You want a Rifleman patch? Oh, that's different.
Let's work on you and then let's refactor your gear.
P.S.: I love my M1 Carbine and it's in as-issued configuration. Never managed an AQT score with it, though, limited to low 200's. C'est la vie.
P.P.S: I like tab away from the stock. To each their own. Never seen it make a big difference either way.