Speak to Italie Cossie on here, he make them.
This is what i got from him,
hello,
the kit has 1000km with new sinchro kit, is heli cut 12 degree and is with big tooth gears and you put the spacer between the two cases and a small spacer on the front propshaft. The gear ratios on my sierra with standard diff ratios 3.62 and wheels 235/40/17 was in km/h:
1st 70.24km/h
2nd 104.km/h
3rd 166.km/h
4th 191.km/h
5th 248.km/h

the kit is really strong and can resist for engines 600bhp +
the price of it complete ready to fit is 1800gbp + postage. I accept paypal as method of payment and for shipment price you have to give me your full adress to take a quote from the courier. You can also send your courier to pick it up no problem for me or i can bring it to a deposit if they have here near Florence where i'm located.