Hate to say this but you're confused on you engine size (460) is a Ford .
454 is the early Chevy size and later it developed into the 8.1 l. and I don't have the conversion handy for cu.in. and I don't know your coaches year.
OK then oil choice , personally if your changing the regular oil at the end of each season , with 3,000 miles, synthetic is just and added expense; and I'm not a fan of changing to synthetic on an engine with that number of miles. Going to synthetic at the first oil change OK, but not after.
5/30 vs 10/30 , most newer engines will have the rec-commendation on the oil filler cap, and the 5/30 is make sure the oil circulates quickly on cold start up.
Both grades of oil are formulated to perform the same at high temperatures, so if the cap says 5/30 stick with it.