Lower a arm, moved forward for caster

[CarlsLQ9SS]

So I moved the lower a arms forward 3/4" and when I put the spacers and shims on the upper a arms I barely get the full thread of the rear nut on it. I used square body a arms and the stock cross member that come on the truck originally in 1971. Are the studs for the upper a arms shorter on the 71 crossmember than they are on the newer square body a arms. I'm worried about getting the alignment right when the time comes. Hopefully someone that has run into this will chime in. I followed an old thread that someone done a how to on and with the spacers that was recommended I can't get any shims in the rear stud on the upper a arm. Here is a picture of what I have as of now.