I'm thinking about changing the engine on my beetle 1600s with a bigger aircooled engine...just for fun

I would like to make the car a bit faster.
Any suggestions of which engine to buy? I've seen a beetle with an aircooled porsche engine which enticed me
but I'm not sure how to get one and if it will be feasible.
So I'm willing to consider a bigger vw air cooled engine.
Please let me know what you guys think....
Thanks
Shaheed