Engine?-A high quality, fully synthetic 10/60. Brand unimportant but don't buy a 'Free grandfather clock with every five litres' Wallyworld special.
Gearbox and bevelbox? The factory specifies some minor discrepancy between the two but again any high quality full synthetic gear oil with a viscosity rating of between 75/90 will be just fine for both.
The filter will be either 76mm/8 flute type or a 76mm/14 flute type. Different markets seem to get different filters. I have no idea why.
I would strongly recommend pulling the swingarm to grease both the swingarm bearings and shock linkage bearings at the first service as they are rarely, if ever, packed properly at the factory.
Also check the valve clearances, they should be 4thou inlet, 6thou exhaust, and balance the TB's. You will need Guzzidiag as well as a manometer to do this correctly.
Do NOT under any circumstances try to change the idle speed by messing about with the throttle stop screw or the linkage rod ends. Read up on the the tuning procedure for W5AM Guzzis and you can't go wrong. There has never been an easier bike to tune.
Pete