Shim-under-bucket valve adjustment

Valve lash on the Cosworth head is set with shims under the buckets, which means the cams have to come off to change them, and the correct shims are increasingly hard to source (owners cross-reference Kawasaki motorcycle shims). Once adjusted the lash holds for 30-40k miles, and the absence of valve ticking is used as evidence the job was done, but the community treats it as a specialist, not trivial, task.