I wouldn't be too concerned with specific measurements. All you need to know is 2 x tensioners... 1 positioned above the water pump on the inlet side and the other down in the tensioner location on the exhaust side.
Then dummy it up; grab the cam belt, came belt covers and position it so that it clears the cam belts. Failure to do so will result in the belt rubbing on the cam belt cover(s); which is what happened to some one I know.
Dummy it up; you can't go wrong.
I've attached the rb30 guide to this threads first page/post that contains a pic and measurements of the upper tensioner location courtesy of that Cobra dude.
http://www.skylinesaustralia.com/forums/in...t&id=132205