Re: EL XR6 diff upper control arm location
some EL's ran an IRS system. The extra holes are to mount this assembly.
If you change it, it won't cure your axle tramp, but it WILL alter the pinion angle, and most likely result in constant destuction of Uni joints...to start with.
There are other items out there to help with axle tramp, but I would start by looking at the condition of your suspension bushes.