Is there a way to adjust the stops in the steering box? If one gets say 4.5 turns lock to lock can the box be adjusted for a little less travel left and/or right? There are stops on the steering arm on the knuckle/spindle which contact the bosses on the lower control arm but wider tires need the steering to stop a little short of that.

I dont believe so, unless you can buy modified knuckles or weld a bigger piece onto it to make contact sooner.

Your steering stops and your number of turns from stop to stop are two different things.

Plenty of places out there that could rebuild your box to spec. I would give them a call.

http://lee-powersteering.com/

If you are using stock lower control arms then it is simple enough to drill and tap the original stop for a 3/8-24 bolt. This will limit turning travel.

I'll backtrack a bit.
I've had front suspension problems since I first bought the car. After I removed the two wooden pieces of 1X2 someone had hammered in between the spring coils, the tires rubbed on the inner fenders. Since then I've replaced the springs, upper control arm bushings, ball joints, rod ends, etc. I've had it aligned and I still don't like the geometry. I still get some tire rub when hitting a large dip in the road. My tires and wheels are a bit larger than stock but smaller than a lot of guys have on thiers.
I thought I'd try other than factory alignment settings but since I've only one shim in the right arm cross shaft the garage could not remove what was needed to get the caster and still keep the camber. I searched for offset ball joints then thought of narrowed control arms. I finally removed the front suspension yet again and inspected all the parts. The lower arms are beat to heck. Both are bent enough to put the ball joint aft of the correct position and the right also seems to be outboard.
I bit the bullet and bought new control arms from Global west. That blew the budget for a couple of years.
After installing the new arms I discovered the lower bump stop does not line up with the bump stop boss on the frame and there is no steering stop on the arms. As I found out from another post (thank you) the bump stops are in three different places in three years. Global west only made provisions for two.
I contacted Global West about the bump stops and steering stops. They had no answer for the bump stop other than different years had them in different places and that they use the steering gear as the steering stop. I think they should have told me ahead of time these arms really don't fit a 68 Firebird. Now I'm stuck with control arms with no bump stop and no steering stop. I asked them about welding the bump stop nut in the correct location and also welding a nut on the arm and installing a bolt and locknut as Dennis did on his original arms. I have not recieved a reply from Global West.
It's a shame to have to modify brand new parts to get them to fit and/or work correctly. In the 8 years I've been working on this car I haven't bought one aftermarket part that fit or functioned correctly.
The next SEMA convention in Las Vegas should have a huge banner "SEMA-HOME OF PARTS THAT DON'T FIT"

Amen! It wouldn't bother me so much if they gave the aftermarket stuff away unfortunately most components are rather expensive. While some of what's out there is high quality, engineering for fit and/or function seems to be an after thought.
The manufacturer will likely never answer your question. They can't assume the liability. Prior to welding on your control arms make sure you identify the alloy so proper post treatment of the heat effected zone can be done, if necessary.

Well I've decided to weld inserts into the control arms for the bump stop and the steering stop.
I hate to weld on these nicely painted arms but other than fabricating a new from bump stop boss I can't see any other option. I'll have to weld something onto the arms for the steering stop anyway.
Where can I buy some blind 5/16-18 weld-in bungs. I've been searching but other than light duty ones at custom motorcycle places they seem non existent.

I feel your pain Blue. You could replace your box with something that has less turning radius there-by not allowing the wheels to turn as sharply. I did an extensive search a few years ago and found a list of different applications with all the pertinent specs on a hot rod site. It should still be there somewhere. Took me about a week to find it but it was a great help to me.

Thanks for that.
I've changed plans, now the plan is to weld a threaded plate to the bump stop boss on the frame and mount the bump stop there instead of leaving it on the control arm. Similar to a stock 67. Then bolt a reinforcement plate to the control arm via the bung that is in the arm. That way I won't have to drill into the arm to install a new bung in the correct location. For the steering stop I'm going to weld a threaded plate to the arm and use a bolt for the steering stop similar to Dennis.

Dennis, if my suspension was that clean I'd be afraid to drive it anywhere. Looks pretty nice.

I'll take some pics and start a new thread as I proceed and maybe give a warning to anyone looking for aftermarket arms, what it takes to get them function correctly. If I knew I would have these problems I would not have purchased these arms from Global West.