Shim over bucket designs usually are accompanied with a special tool for depressing the valve in order to change shims, but the Mercedes (Cosworth) design uses shim under bucket (a little button between the valve stem and tappet), which requires that the cam be removed to change. The old Jag inline six was the same.

My Cosworth Vega is a shim over bucket design (re-engineered by Chevrolet from the original shim under bucket design of the Vega-based F2 engine), and I have the special tool to depress the valves to change shims.

One of the reasons I bought a 2.6 five-speed instead of a 16V was that bloody shim under bucket design. I didn't want to remove the cams to swap a shim.

Bottom line is that you don't need a "special tool" - you just have to remove the cams to change shims!

Duke