I don't understand what the fatman suspension does to the car.
You mention late model spindles, does this mean front steer spindles?
Do you know the difference in positioning between the stock spindle and the late model spindel relative locations in the wheel well?
I think the best advise I can offer is not to purchase any wheels until you have the full suspesion, brakes, and spindles on the car and to take measurements.
usually anytime you look at wheels that fit a late model you need to run a 1 inch to 1.5 inch spacer on a classic
stang in order for them to work...however...a spindle swap 'complicates' the issue.