Great bike! I think you may still have an issue with the vent line at the Y connector. The pressurized fuel from the helper pump is going to find as many ways as it can to the lowest pressure regardless of the length of the path. You'll have fuel squirting out of the vent at whatever the helper pump's PSI is.
I'm wondering, would you be able to just hook up the TT tank to the main tank vent and let the main tank pull the fuel in? If you plumb the main tank vent to the TT tank I would think the vacuum created by the main tank emptying would draw in the TT tank fuel.
Also, if you connected the tanks this way, the main tank would still be able to vent via the TT tank. If the main tank was over-pressurized it would send air into the TT tank which would then bubble up through the fuel in the TT tank and out the TT tank vent.