The way I would do it would be in combination with a bumpstop location reinforcement.
I'd add a pair of Vertical 2" square tubes inside the C-channel of the frame
spaced EXACTLY 2" apart, because there's gong to be a third piece of tubing sandwiched between tying the two sides of the frame together
The flat "crossmember" on the top of the frame on gen2 trucks
is ONLY designed to hang the third leg of the fuel tank strap from it.
Now depending on which way you want to run your trac bar, you'd
want to weld a piece of heavy tube through those vertical square tubes
parallel to the frame and sized to accept a 5/8" diameter bolt 7" long
(you need length for a pair of washers and an elastic stop nut.)
and that bolt will preferably will be grade 8 and fine thread...
BTW, instead of JUST welding those vertical reinforcements inside the C-channel
go a step beyond... cut a reinforcement plate to fit the outside of the frame arch
and with the tubes and plate clamped in place drill through the plate the frame
and the wall of the tube reinforcements
If you wish to have the attachment "hidden" only drill the side against the
frame (two locations), if you want access to the nut drill through both
sides of the tube with your pilot drill then holesaw a socket access hole
on the inboard side.... Bolt everything up TIGHT before you start welding.
I'm a paranoid cuss, I never trust either bolts or welds, I like using BOTH.
It may be heavier but it doesn't break
Personally I'd prefer my inside fasteners to be hidden and after welding
everything up I'd remove the outer bolts and blow those reinforcement
tubes full of aerosol foam insulation.... if something like "Great Stuff"
is filling the sealed void it's for damned sure that water won't be getting in....
But anyway those vertical reinforcements will be more than adequate to
support the lateral load from a trac bar...
I'd be inclined to make one more improvement... a diagonal gusset
out of smaller tube on either side of your tube crossmember
diagonally down to the bottom of the vertical tube reinforcements
atleast on whichever side you attack the trac bar to the frame...
that'll prevent the lateral load from trying to flex the lower edge of
the frame in and out, because the tube braces will transfer the tension
compression and lateral twist of the frame member into a bending load distrubutted across that length of 2" square tubing that crosses to the opposite frame rail...
the frame side pivot point will wind up being a double shear mount transmitting the load through two lengths of tube welded parallel to the frame inside the vertical reinforcing members. I doubt you will be able to attach it to the axle as securely...
BTW, to complete the setup you'll need to cut a chunk of 3-16" plate and weld it to the underside of the frame rail flange to actually reinforce the bump stop mounts
Can anyone visualize what I am describing and make a line drawing?
AD