I relocated my UCAs and I love the change! My '70 handles great! Plus I didn't really like the stock nose-high stance very much. It's the only thing I've changed with my suspension so far, other than replacing the stock components.
From what I've read, I understand you can lower the mounting 1 inch and retain all the stock suspension components. I lowered mine 2 inches, which requires changing the angle of the ball joint so that it doesn't bind and break during suspension movement.
http://www.pro-motorsports.com/art-loweringlowdown.asp
There's some info on the modification. Pro-motorsports also sells a shim to use when relocating your upper control arm more than 1". I was too cheap to buy it so I made mine. Some people also modify the control arms to fix this problem. It seems like a better solution to me if your welding skills are top notch.
Also, I've read in a couple places a recommendation to align the car to different specs than stock (this is after completing the Shelby drop).
1/16" to 1/8" toe in (this came to 0.14 to 0.29 degrees toe in with my 24.75" diameter tires)
1 to 3 degrees caster
0 degrees camber
This is how I had my car aligned and it works great for me.
You can buy a metal template to help you drill the new mounting holes for the UCA. I had two made from 10 gage steel. They also provide some reinforcement for the shock tower. There's a web site with a pdf of the template available, but I don't have it saved. Do a search on this site for Shelby drop and I'm sure you'll find it.
Good luck.