Adding a 911 engine is of course possible in the Beetle, but it will require some modifications, obviously, in terms of air filter, silencer/exhaust system set up and actual fitting in the compartment: remember, the Beetle has a FLAT-4 engine while the 911 has a FLAT-6- you gotta get round the problem of neatly accomodating the extra two cylinders and their associated extra bulk into the Beetle engine compartment, without ripping up metal unnecessarily.
While undoubtedly a Beetle (or any air-cooled VW) in Pakistan fitted with a 911 engine will be a real show-stealer, also do bear in mind that our technicians/Desi "ustaads" are not well-versed with the intricacies of the Porsche flat-6 and spares will not be available, at least until the Porsche network opens up in Pakistan.