Have a read of this thread, cause I can't be bothered righting it all again.
http://www.rollaclub.com/board/index.php?showtopic=17418
As Philbey mentioned I used to use a carter black, which would be suitable for you if you only want to run 8psi. They can only cope with about 10psi max. You would need to use a RR reg too with the asian's as the won't like 12psi of fuel pressure at all, my weber needle and seat would hold the 12psi so I didn't use a reg at all.
Speaking of needles and seats trying to source a higher flow rate one wouldn't hurt. In the twin confirguration they're they're flowing half the fuel of a single carb so *this is only an assumption* maybe these N&S's are smaller than single carbs, if so maybe the single carb N&S will screw into the twin carb.
You should have a decent return spring on any car's throttle, and you won't need to upgrade it for this setup.