1.0 litre box is better for accelaration...but you'll lose a bit of top end.I am going to ask our gearbox man if he could put a bigger cog in there if I feel I need more top end..Not had a chance to see what it will do yet..
you should lighten the flywheel if you're going to use the 1275 engine.And I think you can use a more robust clutch iirc