Hi from Argentina again. I have an RV-8 without rear throttle installed. How complicated is to install the rear throttle to an finished plane?
 
not much harder, if any, than during construction. You'll have to cut and enlongate a hole in the vertical section of the fuse wing spar support to accomodate the linkage between the front and rear throttles but not too hard. The most difficult part is putting it all together since you'll be working upside down and blinde while placing washers and locknuts in a tight space.

Regards,