ugh! I hope you REALLY like all that snow and cold up in mile high area! you should go over with us what you are doing to the replacement subframe for rust preventative. pics of the cleaning and treating with por-15, underbody spray if any, etc. (while, I'll never need any of these tips down here in the piedmont of NC, it's nice!)
I don't think a 1/2" impact will get those axle bolts, perhaps a 3/4" or like said, brace the lugs, and use a cheater bar on there!