I'm with you on not wanting the thin out the tang any. I would probably start by trying to find out how hard the tang is- like by seeing how it responds to a file or regular drill bit. If it didn't seem extremely hard, I would next try hammering it flat on the anvil. If it seems too hard to straighten, I would probably anneal as much as I could without softening the blade area. Then, what I couldn't get completely straight, I would probably let a dark epoxy fill the voids between the scales and the tang. (and maybe you could also fit the scales to the inconsistencies to some degree). I know you wouldn't want to see that epoxy in the gaps on a new knife build, but this is a re-handle on a very old and battle-scarred knife. I would run my plans by the owner first tho to see if that's acceptable to him.
That bolster (?) I see there will actually put some of the stress further out in the ricasso area, where the spine is wider (if it fits tight enough), so I would sure incorporate it into the new handle. plus I would be trying to keep it as original as possible.
Just my thoughts....
If the handle has some flex to it, my solution would be to use micarta or some other "tough" synthetic for the scales......just make sure the insides of the scales are flat, then do a couple "spot" anneals, drill, and use something like Loveless bolts. Once you glue, the clamping pressure of the Loveless bolts, combined with the strength of the micarta or G10 will "flatten" the tang. Let it cure out and finish out the handle.
I've repaired a number of blades over the years that had this issue (a warped tang), and as long as there is some flex in the tang, you can accomplish the method I described fairly easily. A word of caution..... the method WILL NOT work with wood/natural handle material...at least not for very long. Any natural material won't handle the stress, and will either separate at spots along the tang, or crack/break.
Ed, so far I filed the high spots keeping in mind not to over do it I think this blade was edge quenched. I used a scotch brite belt to finish with and I see a quench line about 1/2 up from the cutting edge.
Im considering purple heart with brass pins maybe peened. Ill post some pics this week. Im told this blade wont be used its just deco. Thanks again