Hi Ant from across the pond
Given that you seem to have weight as a priority.
What about a T5 ..... not a normal T5.....Not a Word class T5
but one of these T5's:
http://www.g-forcetransmissions.com/tran_gt-5.asp
Should handle the 347.....will change beautifully, and should be as light as you'd want.
Take your pick of dog or synchro.
You take care