Shorten the Control Arms?

[Mrfixit]

Hey guys,

I just received my wheels and tires for my 68 and am concerned that I didn't specify enough back spacing for the front wheels. I've been pondering my options and was wondering if anyone knows what the results would be if I shortened my upper and lower control arms by 3/8" to 1/2"? Has anyone tried this? Results?

Thanks in advance,