NEF did a run of some Huntsman Combo's, they were all blued and wood. There were 2 different SB1 combos, .50 cal/12ga smooth bore with bead, and .50 cal/12ga rifled bore with sights. The only SB2 combo they had was a .50 cal/.243 Win. These were produced back in the 2003 time frame, I don't think they were big sellers, because they were available for several years. I think they were all from that one run (over run). At least all the ones I ever seen had the plastic sights, which were changed to Williams Fire Sights in 2004. The breech plug is another giveaway, the combos would have been the older 7/8" plugs, if yours is a 2006 it should have the newer 5/8" breech plug. The breech plugs were changed in 2005.
If yours is a stainless steel barrel, nickle frame, with black synthetic stock, it is also a SB1 and can only be fittted with shotgun barrrels or muzzleloader barrels.
There is one way to be certain if your frame is a SB1 or an SB2. If you remove your stock and ther is only one threaded hole in the butt end of the reciever it is a SB1. If there is a threaded hole and other holes (skeletonized) from the investment casting, it would be a SB2, which is very unlikely.
H&R does have some newer combos that use the SB1 frame, but they are 12 ga/.44 mag, and 20 ga/.357 mag. Shotgun and pistol calibers, not high pressure center fire rifle calibers.