there was a time when immobilizers wiht keypad were popular. But I think the only thing they did was interupted a number of electrical connections like you can kill the starter, fuel, ignition.

En example of such thing I just found on google

http://test.daronet.com/ravbariah/product.asp?product=216




Going the way of Transporter is a custom job, which with proper knowledge shold not be too difficult or there might be a kit. And let's remember ford cars that have had combination code on doors for quite a wile now :-)