I just got some global west UCA's (well I did but UPS actually damaged one) I have the 1" drop already, should I weld them up and drop them another 3/8 or 1/2 whatever they recommend or just use my 1" drop holes?
I had the arms in the stock location with upper and lower GW arms and in the Shelby drop location. I could not notice a difference in street driving. Although, this was on a 71 Mustang. I would just leave them where you have drilled.
if I recall correctly, the GW arm length is adjusted (lengthened) to compensate for the lower than stock mounting location to keep the spindle more or less in the stock alignment .... the GW drop is 1 3/8" (memory getting old here, but should be close) .... so using the Shelby 1" drop holes may push the spindle outboard a tad (i.e., increased camber angle) ... but since you'll need an alignment anyway, it can be adjusted out .... but I would guess that the changes wouldn't be severe enough to worry about because we're talking fractions of inch here ....
It would be fine to mount them in your current 1" lower location, but if you're spending the money on the GW stuff, why not take full advantage of improved camber curve and mount them in the recommended location.