With your current a-arms, it wouldn't be benifical. But, if you used an adjustable arm you can make it as long or as short as you want.

The upper and lower arms are differant lengths for a very good reason. As the shorter arm on top moves through it's arc in compression, it pulls the top of the tire in, and increases negative camber. This can be a good thing.

Put the car on jack stands, but make sure the front to back angle is the same as if it were sitting on the ground. On the other side (that has normal alignment) remove the spring/shock, and use a bottle jack to place the hub where the suspension would be if it was sitting on it's tires normally.

Move the tire up 1", 2", and 3" and measure camber change. Then drop the suspension (from ride height) 1", 2" and 3", and measure camber change.

If you use a shorter arm, the camber change will be greater than it is now. Depending on what you have, that could be a good thing, or a bad thing. Shimming for a shorter arm would be more expensive but less work and maybe a better outcome. It also makes it a whole lot easier to adjust the suspension, because you don't have to shim anything. It only takes me about 30-45 minutes to do a complete front end alignment; and I am very picky about it. Close enough, isn't.

Other things to consider is where the tire sits in the wheel well; maybe you want to move it in or out a little. 3/8" doesn't sound like much, but it can really make a differance in tire clearance and looks.

Have you compared the lower ball joints to the chassis center line? Maybe the left one sits further away from the centerline than the right one does.

The point of this rambling thought process is that suspension set up is very tricky. One change affects three others. 3/8" is lot. On my car, 1* of camber only takes about 1/8" of adjustment. And you want to make adjustments in 0.25-0.5* increments. Before you make permanent changes by cutting and welding, make sure you checked all the angles - literally and figurativly. Measure 6 times, cut once.

Friday night the son and I took a straight edge mm reading of the worst side then used the digital anglometer to get an angluar number of the same.
Using InvTan(mm measurement/rim size) we figured out where to go next. Now the bottom balljoint pivot point to where the top arm bolts on is near 12" so we calculated how much had to be cut off to get the desired camber angle. Sounds easy? Wasn't for us straw chewin' bucktoothed hillbillies, but we got there.
Only took about 3 cans to leisurely rip the front end to bits ready to mark and cut.
Today it took about 2 hours to scribe up and cut the plates off and tack them back on ready for my master welder to finish off. To get a neat cut and good lines I clamped a bit of angle iron to the plate and shimmed it out as needed to line up with the scribe marks. I thought of using my 9 inch but decided a grinder would be easier :MECOOL: . So with the 4 inch and an ultra thin wheel I ran along the edge of the angle and got very neat squre cuts. All is tacked on now and I should be able to achieve 2.5 - 3 deg camber give or take a bees-dick from side to side.
A quick anglometer check suggests existing caster of 2.5 pos with the 2 balljoint shims still towards the rear of the vehicle.
When all is said and done I might buy a Longacre or similar caster/ camber gauge as they aren't all that expensive and will be a good toolbox filler. Also learnt that 2 floor tiles with shiny sides together with salt between make excellent turn plates when measuring things up.

So far all is good.
Pic below for those interested in what control arms I am using taken during the disassembly stage. I have tidied up the inner gaurd cutouts and this is also a good chance to add some fat under the balljoint boots and new rack boots.

Thanks for all the input guys.

http://www.comdotau.com/images/fe1.jpg