I use Mobil 1 engine oil - 5W40 and have for 5 years. A friend used Elf synthetic engine oil 0W40.
If you go to a V belt from a W (5 peak) style belt you will probably find it'll slip quite easily due to the reduced surface area.
Can't help with 1GGZE injector or power questions but the hoses are there to balance the pressures in the SC itself. Sudden vacuum in the lobes of the SC can draw the oil through the seals into the SC. Or so I've heard.