Most efficient swap for a mk1??

Hey folks! As you can see from the topic i'm looking for a more efficient and a little bit more powerful engine for my mk1. But i'm not asking for like crazy 150hp+ engines just enough to catch up to the newer cars like maybe 80hp. And since i'm a little broke i want something more efficient. 1.0 tsi maybe? Anyway i'm waiting for your helps!

owning a mk1 you will be broke

You need to factor in the cost of the initial conversion (parts, wiring, complexity, etc.) and the on-going fuel costs (how much do you drive the thing) and VED.

If your car is already fuel injected then a KR might be a simple swap, although if you are on carbs then you might be able to find a KR with a twin-carb setup that will enable you to continue using your existing fuel pump etc.

Used KR conversions complete with gearboxes and driveshafts are quite cheap nowadays if you are patient and look around.

A more modern engine would involve more substantial wiring modifications which you should keep in mind.