The OP said there is an H on the rear face of the cylinder. It strikes me that this is a good time to remember the reason that H was put there in the first place. It definitely was NOT so that collectors many years later can say - "Oh, that's a Highway Patrolman!"
When the parts for the revolver were sent over to the finish shop, the fitter would stamp the H there so the finish shop knew what level of polishing and the grade of finish the cylinder was supposed to receive. A cylinder for a Model 27 and one for a Model 28 were otherwise identical. So, the guy in the finish shop would look at the cylinder. If there was no H, he gave it the bright blue for a Model 27. If he saw an H, he'd finish it in satin blue.
Now, were mistakes ever made? Of course. But the frame and the cylinder were separated at that point. I find it hard to believe that a cylinder would get the bright finish, despite the H, while the frame also got that finish. No, they would both be finished in satin blue.
Also, it was standard practice to refuse to change the finish on a Model 28. And, as has been noted by ken158, the Model 28 was not cataloged with the nickel finish (yes, a few special units were in nickel, but they are in known serial ranges). Is it possible that a Highway Patrolman was finished in bright blue? Sure. Possible, but not likely.
The OP has a very nice looking HP, but I seriously doubt the finish is original.
And, by the way, no one suggested otherwise, but if it were a Model 27, the top strap would be finely checked. You don't have to rely on the model stamp to know it isn't a Model 27, regardless of the bright blue finish.
