If you haven't come across it already
https://www.volvoforums.org.uk/showthread.php?t=160516
Provides a wealth of tips on 'how-to'.
I'd seriously recommend you clean around the filler plug and make sure it will move before you actually try to change the oil - its probably not been moved for 17 years so its likely to be a bit reluctant! When I did my gearbox oil change the first time the only place I found for seals and washers was Volvo
I've just re-read your question and realised you don't have a geartronic box - in which case it's a lot easier. You will just need appropriately sized tubing (too small and it takes forever - too large and you can cause an 'air-lock' in the dipstick tube. Attach the tubing to the funnel and support it so you can refill it without holding - otherwise you will find youself without enough hands.
Best of luck
John