I recently acquired a CZ 550 Safari American with both 375 H&H and 458 Lott barrels. It came with the H&H barrel and I just swapped it out for the Lott. I lubed the threads and then tightened the barrel about 20 degrees past snug. It headspaces perfectly. Am I okay or do I need to tighten some more?

I would imagine that would be plenty. I have a 3 foot piece of pipe by my barrel vise that I use as a cheater bar on my action wrench. I don't think that I could turn a barrel 20 degrees past snug even using that.

Are there no witness marks on the barrels?

Barrels are installed, historically, from less than ten pounds of torque, to over 150, but it isn't like putting lug nuts on a Kenworth. They are very forgiving. You will be fine.
Consider that the M2 50 cal Machine Gun barrel is screwed in loosely and is held by only a little spring to keep it from rotating; Zero torque. Tank Cannon barrels are held by a little key; no torque on them.
Some switch barrel rifles are held on by hand torque.

Thanks. My action wrench--being replaced as we speak--doesn't have a cutout for the Mauser style recoil lug so it was a little awkward to use. That said I had no issue removing the H&H barrel.

I don't remember seeing any witness marks. I guess I should make my own for this barrel.

I do have another concern with this. Both barrels are Douglas and do not have the dovetail for the barrel recoil lug. The stock is factory wood but the barrel lug has been removed. That is probably okay for a 375 H&H, but will the stock hold up without the barrel lug for the Lott? There are two crossbolts.

Yes, with a little work it will hold without the extra lug. Glass bed the action and several inches of the barrel. Relieve the wood around the tang and back of the action to keep them from wedging into the wrist. If you really want, you can also pin the wrist for a bit of extra insurance. A 1/2" hardwood dowel works well for this, or all thread. If the grain flow is good, this isn't likely needed, though.

The important part is tight inletting at the recoil lug. From the factory, it is probably not good enough, and glass bedding is the best remedy. With any gap, the action gets a running start and beats the stock to splinters.

Jeremy

Thanks--I was hoping that was the case. I'll check the grain and definitely do an adding job with the reliefs.

I would install the barrel recoil lug just for insurance. Just cut a dovetail for one, or solder one on a flat, or make one radiusd to fit; lots of ways to do it.

snug and a bit -- 20 deg is about 1/18th of a turn, or close to 1/16 .. so, snug and a bit ... btw, if this was done on a Mauser, and on the torque flange (C or H ring) and not the front of the action, it CAN'T gain headspace (flame proof pants on)

Lots of solid advice here, my local friend had his CZ in 416 Rigby split at the wrist last year a week or so before heading to Zambia.

If you've ever tried to remove a factory CZ barrel you know how damn tight they are. I think they use retired Soviet women weightlifters to install them. I don't think even Olga could tighten a barrel 20 degrees past snug.