RE: hpi rs4 3 twin engine build
i just did a ofna gtp2 with twin lrp .30's
best thing to do would be to tune them one at a time
and the linkege its not hard to do just think it out i used two rods with the ball cup end on them one short and a long one that will reach out to the servo best to be a bit longer you can always cut it and to hold them together i used one of those dubro rings with the setscrew in it to lock them
together around the center of the carbs so you wont have any binding probs. thats all easy its your gearing that you gotta get rite if not
like i see you have about scock gearing your gonna have boat loads of off line power like tire scredding power but your topend is gonna kinda be about the same thats where i was till i went bigger gears on my bell's