Can i see a pic of your car pal?Unless you flare the Arches. I'm running 15x8 et 0 on mine but i have a Wide Arch kit fitted which is 50mm wider.
if you dont go 8" you might just get way with it. but going from 37 to 20 is 17mm wider. measure you gap now from tire wall to lowest point on your Arch. see what you can get away with. Also Depends on how low your Car sits too
Nice car mate ;-)
This where done before the 4 Wheel alignment