The early '99 V-10 was a pre PI (performance improved) motor and had lower output than the '00 and up models of the 2V 6.8s. I would try to find a PI motor donor, maybe even look for a late '03 - '05 to get the improved heads with more plug threads.

The excursion has a 8/99 build date is it a pi engine?
The donor only has 88k and I dont know what would be involved in swapping a later v10. Wiring harness and a tune?

Im pretty sure that all 6.8 EXs had the PI motors. I would think that the harnesses would be the same and you would want the PCM from the PI donor, but an EX donor would be best as the PCM should then be plug and play. After running custom tunes for the past 6 years, I would recommend a good tune for any 6.8 EX!
PI motors will have a "PI" right on the heads casting on the exhaust side, pretty easy to see. What is wrong with the EX's V-10?

The excursion engine is locked up I don’t know why.
It has a pi engine.
The f350 is an e99 npi engine so the intake ports are different, theres egr on the e99 plus its missing coolant taps for rear hvac.
The transmission in the e99 f350 won’t interchange without wiring and a tune because the lock up solenoid but I would like to use it because it has 88k miles and paperwork from a recent rebuild.

I’m considering just using the short block from the donor and buy some of the later 2v heads with the revised spark plug.