"So I opened them up a bit and set them even. I set them so that, when held upside-down, with the float resting lightly against the needle valve, there was 14mm between the top of the float and the lid itself. Can someone verify this number for me? I thought it was supposed to be either 14 or 17mm. But then, it's been 2 years since I tuned a set of SU's..."
This information from Tuning S.U. Carburetters 2nd Edition - Speedsport 1972.
1-remove and invert float-chamber lid.
2-with the needle valve held in the shut-off position by the weight of the float only, there should be an 1/8 to 3/16 in. (3.2 to 4.8 mm.) gap between the float lever and the rim of the float-chamber lid.
3-the float may be set by bending at the crank unless a Nylon float is used, this being a non-adjustable assembly.
I don't know if this will help with your carbs, but it comes straight from the book I've got.
Chris