Brian,
Thanks for the trouble you've gone to on my behalf - much appreciated. Thanks too for the offer of a BA set. I've actually got open ended spanners but anticipate a problem getting one on at the right angle in the available space. It's only going to be needed for the last half turn or so (a bit of plastic tubing will get them most of the way).
I'm being unbelievably pedantic about this because the chances are the blocks will never need removing!
Regards,
Mike