thanks guys.
an out of sync update as i've been pretty rubbish at doing them recently.
I drove the van!!!
1. weaker brake servo has helped make the brakes a bit less grabby
2. New diff has sorted the gear ratios - now only engage 6th at about 50, a great improvement on 30... speedo also says something closer to the truth
3. The noise / power delivery from the carbs is amazing - lower smooth idle makes gentle driving much easier but when i put my foot down it roars straight up to 60 (i wasnt brave enough to go much faster on a first run)
Issue to fix now is that it running really rich throughout the rev range (except idle). I'd drilled the main jet out to 1.6mm as that's what people on the internet reckon is a good place to start, i tried dropping the needles a few rings to make it leaner but that didn't make much of a difference. This morning i fitted 1.45mm main jets, this now has full throttle going lean, not massively so, but part throttle is still very rich.
I've been reading up on bike carbs so have ordered some leaner slow jets (#10s to replace the #15s), unfortunately these will probably take a couple of days to turn up. Plan is to fit these and to drill the mains out to 1.50 - mostly as i don't have a 1.55 drill bit - and to lift the needles back up again.
hopefully i'll be getting close then. there is of course the risk that i am basing all this of a £10 AFG gauge that could be talking bollocks and that it was spot on to start with.