I have vented larger sized discs with 4 pot willwood callipers on my bay, I think its a must when running a high CC engine (Currently 2276cc 160bhp), my gearbox and tyres sizes mean I can in theory on German autobahn's hit 115mph. Stock brakes would not be up to the job IMO!
There are a good few kits worth looking it if you want performance:
In the UK:
https://www.vwheritage.com/shop/bay-bus/AC698505B/front-disc-kit-5-205-t2-64-70-vented-csp/?crumbStartPage=1&crumbStartRow=1" onclick="window.open(this.href);return false;
In the States:
http://www.wagenswest.com/partstore/index.php/disk-brakes/1968-79-front-disk-brakes/1963-70-vw-bus-5-on-205mm-disk-brake-kit-bustang.html" onclick="window.open(this.href);return false;
Hope that helps!