Wooly ESS I can give you some feedback, I have a ZKK-602, (which is the predecessor of the CZ-550) in .416 Rem Mag and a CZ-550 in .458 Lott.
The .416 began life as a .375 and was rechambered by the original owner. The gun was built in 1989 by Brno. The .416 Rem came out in 1988, I am betting that it was bought and then immediately rechambered (to what was then a new caliber).
My CZ-550 was originally a .458 Win Mag and I bought it new (from Williams Lake B.C.) and then rechambered it after about a year of owning it.
The ZKK-602 and CZ-550 both have a safety that is quite similar to the Remington M-700; that is it is mounted to the side and is a 2 position safety.
The difference between these is the ZKK-602 is exactly opposite the CZ-550. On the ZKK-602 you would push the thumb lever forward to engage safety and backwards for fire; the CZ-550 switched this so it is just like the Remington. Back is safe, forward is fire.
The purists argue that this safety should be changed over to the Winchester style 3-position safety. Personally I think that's a lot of hooey! The damn things work fine!
One definite issue on these rifles is they have a conventional sling swivel in the fore-end. This is a ##### on the hand! I had mine removed and a barrel band installed on my .458 Lott. My .416 I removed the fore-end sling swivel. Have not gotten around to installing a barrel band on it.
Also the stocks do not have cross-bolts. I believe this is a good thing to add. I have never done anything with my .416 Rem but I had them installed in the Lott. I have an extra set though and one of these days I'm going to try to put them in my .416 Rem.
Last thing is the trigger. The Brno's have a single set trigger. Lot's of people think this should be swapped out to a conventional style like a Timney, I don't know. I think the triggers on my rifles are fine. i have fired them many times using the set feature or without setting the trigger. They are decent triggers IMHO.
I also had serious issues with the magazine spring on my CZ-550. See my thread about that and my solution.
Barrel is 25". Some people also like to trim an inch or 2 off... not required IMHO...
If you buy a CZ-550 (or a used ZKK-602) and get a few simple things altered then you've got a great DGR rifle. I have read opinions that the magnum length Brno action is the best Mauser copy ever made, even better then the original Oberndorf Mausers according to some.