I have read threads about the HP500 carb motors needing the valve train freshened up at 200-250hr mark. Is that true also with the 540 Bulldog motor or do they use different valve train components?

The bulldogs use a different cam and valve springs and don't have the problem with springs breaking like carbed 500's. They should probably still have the top ends at least checked out for spring pressures and a leak down by 250-300 hours.