You have way too stiff springs. Speedway lists 6 springs now I think. 3 are the stock length and 3 are the 'short' springs. There is also a chart in their catalog. I'd guess you have about 85% of the finished weight on the front now. If you talk nice to them they will let you buy one set and exchange them if they are too stiff or not stiff enough. Just don't scar them up.
Here is the page. You will need to read it over a bit.
http://www.speedwaymotors.com/Mustan...rome,7771.html
I think the 11 inch spring is what you will need.
I have QA-1 coil overs and use a 375# spring. This is too stiff even for my Willys. But it is all that is available for my set up.
Must II lower a-arms need to be about parallel to the ground to be correct. You can get away with a little plus or minus but not a lot. You have a lot.
It's possible you may have to use dropped spindles to get it right..