Congratulations
Wyatt 
I see a lot of good here:
- Barrel band front sight
- Barrel band front swivel
- Direct trigger
- 3 positions bolt-mounted safety
- Recoil shoulder on the front square bridge
- Not sure what our canadian friend means, but, to me, the bottom metal seems well bedded in the stock
- The barrel is of appropriate contour
- The stock appears appropriately beefy and deep-bellied. I do believe that it may very well be a B&C -- it looks exactly identical to the one I have on a .375 -- and these are really good stocks. Pulling the action out of it will tell you instantly if it has the full metal bedding block or if it is an earlier one with just metal pillars as I suspect may be the case. In either case, they are indestructible.
So, OK, in a perfect world the rear sight island would be integral (not much that you can do about that), and the rifle will likely benefit (from an aesthetics perspective) from cerakoting the stainless barrel in a matching black, and plugging or replacing the bolt handle, but this is not a big deal. I would agree that it is likely an Ed Plummer rifle, from before he sold AHR to Wayne, and Ed knew how to put rifles together.
The tooling marks / paint scratches on the stock likely indicate a home-restock with a drop-in stock (Ed's originals were typically wood laminates, and in any case he would not have left imperfections like these come out of his shop), but touching them up is really not a big deal.
As to the caliber, sure it is not very common, but it is good. Most folks comment on the rim being less rebated than the .500 Jeff, which is huge in terms of reliable feed, but just as important is the fact that the cartridge is also longer, which facilitate a lot feeding from the long (Rigby length) CZ 550 action.
Unless there are hidden vices (always possible with second-hand rifles), it looks to me like you have a bomb-proof DG stopper ready for hell or/and high water (assuming it feeds, which I am willing to bet it will because Ed knew what he was doing), so I would likely think twice about letting it go, assuming you have some brass and you reload.
PS1: the one thing I would suggest, is to shoot it a couple times without a scope first -- it is a kicker -- and when you mount one, to push it as forward in the rings as mechanically possible, without giving a thought about "perfect" eye relief distance. It matters not whatsoever if you see a fuzzy black ring around the sight picture, it has no bearing on point of impact, but it sure reduces the risk of being clubbed to death during recoil. Make no mistake, this will recoil A LOT more (almost twice as much actually: ~120 ft lbs vs. ~65) than a .416...
PS2: If it is a B&C stock, there is a hollow compartment in the stock that you can access easily by removing the recoil pad. Pouring lead shot-enriched resin in there will add mass, makes the rifle balance better (it likely has a heavy barrel!) and it will cut recoil meaningfully. If it is indeed 10 lbs, you likely would want that rifle to gain at least 1 to 1.5 lbs.
