He'll be fine with the H&R/NEF in SASS shoots, they are a more relaxed bunch than the guys who shoot NRA BPCR about this rifle.
Wesson, of Harrington and Wesson did indeed make a breakopen action in the 1870's. Problem is, the current H&R?NEF model does not share its ancestors action in detail, as a result the BPCR boys get quite upset about it. Seems they want original or actual replicas of rifles made prior ot 1890 or so. Funny thing though, the 1885 Browning has not one leaf spring in it, while one'd be hard presed to find an 18885 Winchester Hiwall with coil springs. Go Figure. All this is too bad, a lot of otherwise would be players are out of the game. Some clubs/matches do allow what they call fun guns but your scores won't count for beans with NRA sanctioned BPCR.
The SASS shooters on the otherhand seem to love anything that is old timey in nature, and the SB2 fits that bill to the tee. Is it a true replica? No. Is a authentic to the period? Certaily in spirit, and with it's Wesson predecessor, even in concept. So the SASS boys turn a blind eye, in the spirit of having a bit of fun. Of course they accept the Ruger single actions revolvers too and nothing about them except the concept and the apperance is authentic.
A lot of this is why I quit shooting the games back in the late eighties. They became equipment races. The SASS gals and guys seem to have the right approach, if it is true in replication or in spirit, bring it along and let's play. More power to SASS!!!! May they introduce many thousands to the shooting sports and the fun of shooting in general.