Trying to use a timing light to set ignition timing is extremely difficult given that the pointer on the timing cover used for alignment with the notch on the crank pulley is at the bottom of the engine.
Tom Colby at Speedwell Engineering https://www.speedwellengineering.com/ignition-timing-pointer-kit/ makes a stainless steel pointer that can be used to move the timing process to the top of the pulley. This is from the Speedwell website:
A duplicate of the 1968 Works BMC Le Mans timing pointer makes for timing the ignition system much easier by moving it to the top side of the engine. The Polished Stainless Steel Pointer (with a flanged nut installed, eliminating need for washers!) is easily installed by removing a timing cover bolt and installing it in place of the bolt. Once top dead center is achieved, just apply the adhesive backed laser-etched stainless steel timing tape to the crankshaft pulley and you’re ready for precision timing with a timing light. Complete with instruction sheet. 100% Made in the USA
This is a short video showing the installation of the ignition pointer. Installation required draining the coolant and removing the radiator.