Bassett Lowke Uniflow poppet valve engine

It is beautifully made, and relies on a crankshaft driven cam to actuate the inlet poppet valve. Its another uniflow design. The cam has slipped on the shaft so it currently doesnt run. I need to work out how to adjust the timing, the cam is hidden between two ballraces in the main casting.

It dates from around the early fifties. Heres an ad i found in a 1952 edition of ME–

Be seeing you
Sp.