Mustang 2 suspension is far too light for a 3/4 ton truck. A better solution would be to use a complete crosmember from a full size '73-'87 Chevrolet truck, which not only has the load capacity, but will also have brakes capable of stopping a 4000# + truck.
I think longbox is considering a pinto ifs when he says it's too light for a 3/4 ton. I installed a Heidts system and it works well for my 1951 3/4 ton. Actually there is little difference between a 3100 and a 3600 AD except heavy duty springs in the rear, heavy duty front end, and rear rails 11" more narrow than a 1/2 ton.
When you swap the original front end for the IFS you basically have a 1/2 ton.
