It is a clean bus with a high roof and side storage compartments. To me the seats and above seating racks adds value but all of that is going to be removed for a conversion. It is an 11 window bus so the low seat count is misleading.
The gear shift indicates a AT545 trans which would give it a 5.9 Cummins. A picture of the engine would help. That wouldn't be bad but you may have a heavy bus if you do a major conversion.
The mileage may actually be accurate but needs to be verified with repair/maintenance records. Since it is probably a reseller, records may not be available unless he went to the church it came from. Also, age alone can affect some repair/maintenance needs.
The tires have good tread but may be old and need replacing. You would need to get date codes from the tires.
The existing paint also helps for value if you can buff out the lettering.
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