1985 D150 "Mr. Curtis" race truck with a 2015 6.4

I don't any more think it will fit.

The track width on a 1500 is 68". Add 2" of wheel offset and you get the front axle width of 70".
Substract 5.3" (total shortening required to get the rearmost of the front suspension crossmembers between the frame rails) and you get
a one inch smaller track width (64.7") compared to the original setup which is 65.7".

All in all it leaves me with a front suspension almost 6" too narrow.

Moving the lower control arms outboard will probably move the location of the spring out of reach of the upper spring cup on the factory crossmember.
Argh!