Miles,
go to
www.subaruparts.com. Click on "parts" then look for the line "if you have an SVX, click here" at the top.
They have an interface that lets you shop for parts with diagrams. You don't have to buy to fill your shopping cart and get pricing. That will give you a barometer, if you decide to buy your parts elsewhere.
If I were goint to tackle the t-belt and water pump, I'd go ahead and replace cam and crank seals as well.