I thought you had a 1275? If so (unless it is a genuine Cooper S block) you'll have to take the engine out, and split it from the gearbox, to do the followers.
Couple of days ago I wanted the cam out of one of my spare 1275 non S engines to see what it is.
Stood engine upright, clutch end down
Removed camshaft, good condition 544 fitted !!
Thought I'd have a look at the followers and managed to remove them all with one of those larger telescopic magnets.
The one I did drop simply landed on the oil pump and was easy to get hold of.
I wouldn't have cared if any did fall in and dissappear which is probably why none did !
But it struck me that if I wanted to fit new ones I reckon I could.
Just one of my 'It's a forum and all knowledge is good' type posts