I decided to deal with the master cylinder mounting first.  I pondered over night and decided that I really need to cut out the metal and replace it with fresh metal with the captive nuts in the correct place.  So I took an angle grinder to my lovely Healey Ice Blue chassis and then got on with it.

I guess that a benefit is that I will have a little piece of my Healey Blue car in the garage for all time.

I cut out the correct shape and welded some nuts in the correct place before welding it back on to the car.  A few times the Healey Blue paintwork caught light and it hurt every time.  Once done I painted it with some grey POR15 paint and then went for a curry.  I ground down the welds where the aluminium spacer goes but left the rest in hope that the strength of the welds remains.