Welcome to the IDI diesel forum!
The 6.9 IDI and 7.3 IDI are very similar and most external parts can be swapped between the two.
Find an '86 or '87 6.9 engine. Have the 6.9 rebuilt and install that into your truck.
Why? The 7.3 is a bored out 6.9, so the 7.3 cylinder walls are thinner. The 7.3's are prone to cavitation (when the cylinder walls develop pin holes and leak coolant into the cylinder). Don't bother with a rebuilt 7.3 because the cylinders are sleeved. Dave S. went through 3 rebuilt 7.3's where the sleeves were incorrectly installed. Finally, he built a 6.9 and is doing well. Oh, by the way, his 6.9 is far from stock and holds up excellent.
I don't have a ballpark number for a rebuild. However, members spend about 5,000 if the machine shop does the machining and you do the assembly.