I don't think GM added the crash bar in 08 for any sort of frame enhancement...its way too flemsy to be called a crossmember. Also the way it attaches does nothing to actually stiffen the front frame rails. I think it has more to do with protecting the lower tank of the plastic radiator, or possibly adding a tad more tinfoil to the already tinfoil front bumper to "up" the impact rating. Whatever it is...the 08-up bar is useless as any sort of "enhancement" and I find they make great pull-up bars if you screw them to your garage ceiling joists.
Back to your fitment issue...
I think the root of your problem with your frame rails moving around, is the lack of any crossmember forward of the motor. You were probably okay with the IFS because the factory rack & pinion crossmember (along with the drop-out diff crossmember), makes for a pretty stiff package. But when you did the SAS...all that got removed, and the only real crossmember remaining was the two motor mounts and the engine block. Then once you add the steering box (instead of IFS) you are doubling or tripling the lateral forces on the frame rails. You can literally push & pull the frame rails apart from each other, making for a very bad scenario. This is a common issue with all big-tire 4x4's and Jeeps are famous (especially uni-body XJs) for this same problem. No doubt the stock H3 front bumper does nothing to control the flex.
I've been running a THORparts front bumper for years...both before and after the SAS. It never occurred to me how flemsy the frame would be without it (after the SAS). It is essentially...a bolt-on crossmember, and I sort of ignored any frame flex issues because I knew the bumper would account for the missing crossmembers. But, now that I have seen how crooked your rig is...I think anybody contemplating an SAS needs to address this problem by using a thick, strong, aftermarket front bumper...or by welding-in a crossmember like you did. You do some pretty extreme rock crawling, so its not a huge surprise that Squeaky is tweeked that much. What is a tad surprising, is how easily it can be manipulated with nothing more than a ratchet strap. Good job, and let us know if you can feel any difference in the steering, now that the frame is secured.