For about the same price of a set of tyres, you can fit the following to a regular 4 cyl engine and have greatly improved performance and economy:

Performance Cam: Better top end and torque, no loss in low end torque at all.

High Compression Cyl head : Increase compression to around 9:1 without affecting reliability

Higher flow carb like Weber 34ICH, 36 DCD or Zenith equivalent
The carbs are no longer available new - or very difficult to find. The only carb options are a new Chinese or genuine Zenith carbs which work very well but are not performance enhancing above the standard

Performance exhaust Manifold: Branched and tuned exhaust manifold to replace the cast iron original
These manifolds are no longer readily available

Free-Flow pipe work and silencer : Help the engine get rid of old exhaust gasses better.

Out of the above list the cam upgrade gives the best performance increase, the higher compression head is second in line.

The carb  mod is worth the extra money, especially if the existing carb is a Solex.

For more details please contact see what LandyOnline Workshop offers, and contact them for more information.