serpentine belts, impellor, fuel filter, oil filter, heat exchanger zincs
Jim, nice boat, nice engine. The real beauty of your Beta is that you are NOT limited to spare parts like Yanmar owners are. Indeed, it is my understanding that Beta actually encourages its owners to find spare from Kubota tractor dealers, 'cuz it's a Kubota block. That's what I've been doing with our M25.
Impellers: buy locally or through
www.depcopump.com There are few others, too, for good pricing. Depends on what pump you have, but we've found the Oberdorfers far superior to the Sherwoods.
Fuel & oil filters - do a Google search for "equivalents" or make up your own table. Buy them at an auto parts store.
HX zincs - figure the right size for you HX and find them locally or at West Marine and buy a dozen, you'll be good for many years. Check them every three months until you get a feel for how long they last in your particular waters. Sendure & Seakamp make HXs, bookmark their websites.
Don't pay marine prices for stock items. Ever.
Good luck.
You may be interested in this, while not for your engine, it has a lot of valuable info:
Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too
http://www.c34.org/wiki/index.php?title=Diesel_Engine