I just redid the front and rear, upper and lowers on my 67, with Global West Tubular arms, UMI "stock height" coils, and Bilsteins. Yes, it all changes the geometry. If you simply push down on the front of your car, you can see the camber and toe in changing... I believe they call that bump steer.
I can tell you that when I just ditched my 55 year old coils, it completely threw out the alignment. It raised the front at least 2".
Personally, I love GTO's that sit high and level. I realize that's subjective. My 70 Vette sits high, too. In my experience, a well maintained and cohesive configuration, works better than simply lowering the car. If you're going for aesthetics, then there are many solutions, but if your concern is handling, then try and find an existing setup and follow their guidelines or components.
Hit up the Global West website. They have many A Body videos and they race these cars. They also answer the phone and are extremely helpful. I called them and told them that I was going to have trouble installing their parts, because of my headers. I figured that theyd laugh at me. They actually told me how to do it and save about 6 hours!
Army, when you instal front tubular upper a arms, do you use shims or is the new camber geometry already engineered into the unit itself?
I'm thinking about picking up a budget set like this 1964-1972 Chevelle Monte Carlo GTO Heavy Duty (4) Tubular Control Arms A Body GM | eBay
and replacing all ball joints with MOOG K5103 and K5108
Cannot afford GW, unfortunately.
also, did you have to "massage" the lower control arm into the frame on your 67 or was it an easy fit? I've read some of these overseas kits are a very tight fit requiring some minor grinding to squeeze them between the frame mounts.