ET 45 will stick out from the arches a bit I think...or is it the other way around. Ah I can never remember. I think the smaller the ET number the more the wheel sticks out.
i have a classic and looking for new rims i currently have 17x7 et45 with about 3-4mm on the inside before it starts rubbing on the inside at the coilovers.
im fairly sure that if you go to 17x8 et45 it will mean that extra inch in width will be spread across the wheel, so you will stick out half an inch over the fender and half an inch towards the coilover it will be a close fit if it does fit.
im bad at explaining stuff but i hope it helps.
ive been looking at this stuff only for a week now and according to what i read it seems right but i hope someone corrects me if im wrong.