O.K. Serious & polite now.
You mentioned frame stress. I can see you having probs with twisting due to the mechanical leverage that those much longer mounts would create.
These frames are not the best when it comes to strength. They're not all that bad, but not all that great either.
They suffer a prob called 'Beam Walk'. The frame sets up a resonance between the 2 rails at certain speeds.
There are more than few threads on here basically concerned with..."My truck has a vibration." Usually it occurs between 40 & 50mph, disappears above that, & then reappears again at around 70mph.
GM is aware of the problem & they actually have a suggestion to cure.
Get this. Their 'solution' is 500lbs. of ballast! Gee thanks! That's just great. But, not very practical. It does reveal that these frames are somewhat lacking when in stock configuration. Start messing with monster suspension lifts & things start to rear up their ugly little heads. GM only designed the frame to meet the minimum basic standard. Of course it's the same ole same ole. One thing leads to another when modifying.
There is something that you can do, though.
#1. Box the frame.
From the rear cab body mount back to just past the rear shackle hanger. This is a bit of a logistical nightmare, as you have to work around all the stuff mounted to the frame. It has been done before, though.
If you were to do this, then the flex points would become the crossmembers. I'd suggest plating them on the topside.
But, once again this moves the stress to other locations, that being where the crossmembers attach to the frame. So...Those areas where the bolts go through the frame would need to be plated with additional steel.
Then there's having to reroute all that stuff running inside those open frame rails now. Otherwise, how the hell can you get to all that when it's enclosed inside the boxed rails.
I have actually seen where someone took another set of frame rails & welded the left one to the inside of the right one & vice versa. Wish I had taken some pix. It was actually done quite well.
But, all this is adding a **** load of weight. Especially when utilizing a second frame. While that's not all that bad, there is another way to strengthen up that noodle of a frame.
#2. Instead of boxing the whole frame from the cab mount back, trusses could be welded in on the open side of the frame channel. Sort of, kind of, like a bridge. A series of bars or rods in a 'V' configuration, also running from that rear cab mount to the rear hanger. Spread that stress out. This would not only stiffen up the frame, but it'd be lighter than boxing. Less B.S. dealing with all the stuff connected to the frame, too. I'd still plate those crossmembers, though.
I could see that amount of lift really giving the stock frame rails a bad time with the added stress & torque, especially with the not-so-great rep that they already have under 'normal' circumstances.