Harry,
Sounds like you are in a real jam with the dealer situation. I will try to help, but I am no expert either, I know enough to be dangerous!
First, It sounds like the PB kit is complete the way you have it, like already said, it's main purpose is to provide a hookup for a backhoe, and you do not want the 3PH working with the BH on.
Second, Its sounds to me like you need the 3rd SCV kit to operate your toplink and your tiller. The handle for the 3rd SCV will go right in your fender alongside the 3PH lever. I cannot offer part numbers for this kit, but I think I've read that it is about $250.00 or so and fairly easy to install yourself. You could also hook your splitter to the 3rd SCV couplers, and bungee the handle down so your have a constant flow so you can operate it like you do now, and your 3PH will still work.
I think this will be the cheapest solution to your problem.
There are ALOT of 4310 owners on TBN, I hope somebody will chime in with the part #'s and prices for you. If not, you can register with
JDParts and try to look it up yourself. Or go the main JD site, then to the configurator to BUILD YOUR OWN, and add the 3rd SCV kit to get the whole goods parts number...
Also, try searching TBN for "4310 Remotes", I am sure you get alot of hits. Just be sure to change the date range to "ALL POSTA" as it only defaults to one week.