Scenario 1
This is basically KCM Naruto (no clones) vs Killer B who can only go up to V2, which means Naruto would win this. Even without clones, he still outspeeds B, and he has FRS and Chou FRS, which will undoubtedly kill B if they land, especially the latter. To buy time for the Chou FRS (If one believes that the normal one won't kill him) he can use one of the Boss Toads.
Scenario 2
Naruto might win this..but I don't know. If B ever gets off his Bijuu Dama, it'll be GG Naruto...but, Naruto has ways of stopping that from happening.
-If FRS hits him before Bijuu Dama charges up, then he obviously won't be able to charge it up while taking the damage from the explosion of the technique. I'm also inclined to believe a big enough or a decent amount of FRS should kill him even when in Full Bijuu Mode.
-Ma and Pa can temporarily paralyze him with Frog Call, allowing Naruto to charge up Chou FRS and get a direct hit right on Hachibi.
B has a high chance of winning here though.
Bee tanked his own Bijuu Dama, there's no way a Chou FRS would kill him, KCM Naruto has no counter to Bijuu Hachimaki, so he loses.
He didn't tank his own Bijuu Dama, he got wrecked by it and forced out of Bijuu Mode. Chou FRS would severely impair him and more FRS would force him out of Bijuu Mode.
Bijuu Hachimaki only blows you back, its not going to deal any damage to him at all, so telling me he has no counter to it isn't helping you here.
He doesn't need to kill Naruto with it, but it would leave Naruto vulnerable to take a Bijuu Dama, I didn't say he tanked it with no damage.
Tanked means you take an attack with little to no damage...at least that's how I've always used it.
Then I guess B wins.
Itachi's Susano'o didn't take Kirin with no damage yet people say it was "tanked" (I don't know if you do, but I've seen a lot of people saying it).