weld in disadvantage - you're making an irreversible change to your classic truck.
bolt-in disadvantage - bolts can loosen and must be monitored
You can also state these two aspects as advantages, depending o what your priorities are.
The weld-in may also obliterate your VIN on the frame. I don't know about AD trucks, but that's an issue with my TF, a 57.
regards,
Leon