What did you do for rims...
 

You are not going to get a 10 inch wide rim work. Friend has 68 convertible with 17 by 10 with a 275/40/17 tire and they rub a slight amount on big bumps running just leafs. With the air ride I think it will do the same unless you clearance it in more than a few areas. 68's are about 1/2 to 3/4 of an inch more narrow on each side than a 69.

If you are gong to run it low with 20's, I think you will need a 9 inch wide with a 265 width tire.

On my 69 with the fender lip trimed I could not get a 285/19 to work without a slight mini tub...and again the 68 is more narrow

any build pics for us KD? :D