The swap is relatively inexpensive and not to time consuming. Used 6.0
intercoolers can be had on eBay for around $100-$125. The 6.0 IC is
about 30% larger than the 7.3. The original 7.3 PSD intercooler
measures 30x18x2 and the 6.0 PSD is 30x21x2.25.
This article will hopefully give you some insight on how to adjust your
fuel injection pump on 88-93 7.3L Non-Powerstroke, IDI. This will
probably work the same way on a 6.9L Navistar(Ford) engine as well.