Hiya Kerry,
Welcome along.
I'm not 100% sure but I think the Bis & air cooled ignition barrels are different.
The air cooled cars have a cable operated start lever under the handbrake therefore the ignition barrel has only 2 positions (on & off), this part I'm sure of.
I've never started a Bis but I think the ignition has 3 positions (on, off & a spring loaded start position), you would know more about this than me.
If what I've said is correct it means that the Bis ignition barrel could be fitted to an air cooled (the spring loaded start position would just be redundant), but not vise versa.
The only way you could fit an air cooled ignition to a Bis, is to wire in a separate start switch on the dashboard. Probably easier to find a Bis ignition barrel with a key, somebody on this forum must have one kicking around.
I hope this helps, Steve. :smt002