When I hear an uninitiated VW owner express a fond desire to install a Porsche engine in his bug, I know its because he does not understand whats happening in the VW high-performance field. And he's probably never priced Porsche parts either. Porsche owners who become performance nuts find that there's very little equipement for their four-cylinder engines (which aren't so powerful, it turns out) and turn to an expensive 911
When you install a porsche engine into a VW sedan, all of the engine tinwear must be cut away at both the sides and the back. The tinwear must be reconstructed after the engine is installed so that none of the exhausted hot air from the engine will be recirculated through the cooling system, just as you have to do with the VW engine.
The Porsche heater boxes do not fit, so new ones must be fabricated by grafting on VW parts. Because a Porsche muffler will not fit into a sedan, you'll have to modify its width or buy a special VW extractor exhaust with Porsche flanges and dimensions.
You may discover that there is a valve cover clearance problem when you measure the engine width. This requires additional body modifications.
Naturally, you'll want the starter and flywheel gears to mate, so you'll have to get a Porsche flywheel with the appropriate number of teeth.