would a 32mm filler neck dimension be sufficient anyone know? What is 'standard' on most cars? I am adapting a m/cycle filler and cap...not made the tank yet. 32mm is the dia. of flexi fuel tube i can get easily.

Try this thread.
I asked similar question a while back.

http://www.locostbuilders.co.uk/viewthread.php?tid=13102

John