EM006 MAC ENGINE

My exhaust valve lifter does not operate. When lifted the flat on the spindle does not impact the push rod quadrant. - Keith Reynolds 29/11/2003

It's not clear if you are looking at the valve lifter inside the timing chest ot from outside, but you can check from outside as below.
The most likely reason for the valve lifter not lifting the valve is of course that the cable isn't turning it round enough. It has to turn a lot so to check, first put the engine on compression and turn the lifter at the timing chest with your fingers or some device attached directly to it until there is more resistance than just its return spring and observe how far it goes. Then move the engine nearly a rev so the exhaust valve is open and you should be able to turn the lifter a lot further round.
If you can, your cable inner is too long.
If there is no difference and you can turn the lifter all the way with valve open or closed, then someone has modified the follower to remove the ear that the lifter contacts (perhaps to lighten the follower for racing) or a non-MAC cam follower has somehow been fitted (all lifters were the same). - TW 29/11/2003