Lifters or Tappets V1

Can anyone tell me is it a costly job to do the lifters on the V1 Engine or even if its possible to do them yourself?

Valve clearance is a bucket and shim arrangment on imprezas,

The valve clearance has to be checked with a feeler guage then the cam removed and the shims changed for thicker ones.
You'd have to really know your stuff and have tools like, micrometer, feeler guages, torque wrenches etc.

You might be best to leave it to a garage, to be honest its not the easiest job with the engine in the car

So it would be a costly enough job? I just cant stand the noise of the tapping away. It makes no difference on the drive of the car just the sound but i hate driving anything if I know there is any issue