Thanks for the reply, the engine had been sat for a few years whilst I built a car around it and has always been quite rattly. After I got it going again I felt it wouldn't do any harm to clean the lifters. Only 2 of the 8 exhaust lifters could be removed/rotated with the sucker. The other 8 were firmly stuck in their bores and wouldn't rotate or lift out with the sucker. The only way I could get them to move ( out or rotate ) at all was with long nose pliers. If I push them back in again to their running position I am still unable to move them in any way with the sucker.

If I fit the lifters from the tight bores into any other bore they are fine. If I fit another lifter into one of these 6 I have the same issue.