james5 is the man to see ,he ran a vnt on one of his old c1js ,i do believe there mental !!!!! 
Indeed I did run a VNT on my last C1J the same spec VNT you have on yours BLUE85GT they were made by turbo developments as a Limited edition thing there were 2 version's. Once they are setup for how you want they are awesome. I set mine up so I had full boost @2500rpm and it would just keep pulling over 7.5k rpm's +
You can basically adjust the VNT to come in anywhere in the rev range you want :mrgreen: but you must have the fueling and I would also advise you to run full retard on the TDC sensor aswell and monitor for det / knock. My main problem was det anything over 20psi and the engine would want to det prob didn't help with the engine being high comp.
I would love to help you setup matey but we have another baby due in 6-7 weeks so unfortunatly I have no time I can assist online and on the phone but not able to pop up and help out unfortunatly. I am sure Markey Mark BD will more than happily help you out top bloke been around the 5 gtt for many years and has experience with VNT's as he also had one aswell.