To help with your desire to add a third remote valve to a 7030, there are a couple of things to consider. #1. All 7030/7050's originally had remote couplers clear up high under the SMV sign. Are your current couplers like that?? or have they been updated to the lower (under the left lift arm) outlets ??  #2. Do you currently have cables controlling your valves?? or solid linkage ??  Any way you do it, you will still need four tie bolts that are long enough to go thru all the valves. That issue doesn't change.