The T444E is a strong engine, yet at 280k+ miles, what they call the b10 and b50 (https://www.google.com/search?q=b50+...4dUDCA4&uact=5
) it's probably pass the b50, meaning you really want to make sure it's thoroughly inspected. I believe my T444E b50 is at 200k.
It's HP ranges from 190 to 250, so knowing which it is, is important. Although the 190 is small, in a cut-a-way it would be fine.
The tranny is important to know which you have. Some are known as solid, others with beyond the normal inherent issues of all things mechanical.
It seems to small a vehicle for a Allison 3000, and the 1000 and 2000 were not yet out in 1999. So, it's probably something like a:
AT545 - Yellow (smaller, doesn't take much abuse)
MT643 - Green (biggest issue is the electric modulator, but it's addressable...ask me how I know)
Beyond that, cut-away vans are just that, vans. 280k on any vehicle is going to mean there is wear and tear on the major systems. Brakes, suspension, steering, wheel bearings, body (damage / rust), etc.
These items can add up fast!
Again, a thorough inspection is important.
Best of luck!