Head down to a place like Trotac in Victoria, and they can set you up with a threaded heavy stainless solid rod and heavy stainless rod ends etc. The Yami dealer will have the mounting plate for the kicker (that's where I got mine when I got the new kicker) and you can make a mounting plate for the main out of plate stainless. That's how my ball joint tie bar system was put together, and it has lasted almost 17 years now with no problems. As someone mentioned in a previous thread, put a nut on the threaded rod before you cut it to size so that when you remove the nut it cleans up the cut threads, so you don't cross thread when you put on the ends. Measure twice and cut once and don't make it too short or too long and exceed the adjustment amount in the ends necessary to align your motors correctly.
Mine is mounted all the time and both motors can go up and down together or independently with the tie bar in place and mounted to the front of a Yami 9.9HT and a Merc Opti 225 both of which are way out the back on the pod. The way the pod is designed and the motors mounted and spaced, it is an almost straight line and not greatly off level for the tie rod, which helps keep within the vertical range of the ball joints.
In your situation I might be tempted to go back to the dealer and complain first. Especially if they installed both the motors and the tie system.