There are 2.9L drop-in long blocks available for your VR6 car. With some serious long green you can get an R32 engine into that bad boy. To use a motor different that the VR6 you'll certainly need to get the trans out of whatever donor car you find your motor in. There were plenty of Syncro 4 cylinder cars in Europe and Canada that will work for donor cars. I'm not sure about the rear gear ratio from VR6 to 4 cylinder, but I'm sure you could find out from some of the websites. If the ratio is not right you could burn out your viscous diff pretty quick.
I heard in Europe the New Beetle came with a VR5 engine. I don't know if this would be attractive to you, but the bellhousing should be the same. I don't know why it would be different.
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