I have a 2003 280 with twin 4.3 mpi 220 hp each, it cruises nicely at 3400 rpm wish it had twin 350 mags. Think single 350 would be considerably under powered. In 2003 the 496 was the base engine and twin 4.3 were up grades.
Nest advice hang out with the life long boaters, they are a wealth of knowledge. I have a 280 sundancer with twins. Spent a few hours on the water with an old salt, he taught me a lot, also was great resource for maintenance
