Stuey of course you can, i have just finsihed cellotaping up your parcel my mum is posting tomoro morning, you will love!!! i will have to send it seperatly now, i have you address, so no worries m8.
The Bis has a syncromesh gear box, the fiat 500 had a crash box which meant double declutching when lowering gear. as the 500 and 126 aicooled had same engine (diff CC) the gear box was the same. so the answer to your question is no the BIS has a differnt gearbox. I havnt answered that very well, was trying to add a bit of technical for future reference.
regards Chris