Either Aisin (OEM/Volvo) or HEPU water pump would work fine, the kit should ideally come with new bolts and gasket (my memory was that the OEM pump may not include the hardware, and the HEPU gasket is less nice, but also serviceable). HEPU seems to cost under $50 from FCP Euro; given the amount of work involved maybe not a bad idea to order one and see if it's worth replacing as you take things apart. Water pumps should last long time provided the coolant has been changed regularly and is at proper concentration... I'd only use INA (OEM) for the roller, and OEM (Aisin) for the tensioner. Any good quality belt will do (Continental, Gates, Volvo...) Elring seals usually sold at FCP or IPD are inexpensive and reasonable alternative to pricey Volvo seals. I would also replace the thermostat (Wahler/OEM Volvo) if it hasn't been changed recently (while the cooling system is drained of the coolant, it's not too much of a detour). Parts are easily available (timing belt minor/major kits..): FCP Euro, eEuroparts, IPD...
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'98 965