As Bill Goforth mentions in his book, nothing is concrete when it comes to H&R serial numbers! Some of them where his best guess at the time, since he was the only one really digging deep into H&R.
And as CZU mentions, it might be under the top strap, which can be easily seen with the cylinder removed.
I have a couple H&R pistols that don't follow what should be protocol, but with the barrel markings and the frame, and that there are no caliber marks, I would still say it's an Auto Ejecting 2nd model.