Here are some snapshots of the gearbox that will fit on the lower shaft of the secondary, replacing the lower bearing as that bearing is part of the gearbox. The gearbox is slid up the lower secondary shaft and secured in place via the existing 1/4" bolt (the bolt that fixed the tr belt pulley to it.), The gearbox runs spiral bevel gears at an angle so the tail rotor drive shaft will go down the middle of the boom. There are 2 intermediate inline bearing mounted to an aluminium plate that bolls to the bulkhead that carry the swing arms for the belt drive system. This gearbox has an oil pump on its bottom that circulates oil that is passed through an external oil filter. I have more information on my "Rotorway Mods & Upgrades - Australia 
https://www.facebook.com/groups/1523964747814153

I thought I would post where we are with the tail rotor upgrade, nearly there, some cooling fins to add, oil level sight glass to add, filler / breather cap to add, chip detector to add and a few other incidentals changes as we refine the design, but it is looking good. (the RW hub is just for appearance sake as the buyer will use his / her own RW hub and blades etc.
With this design I have the option of being able to slightly rotate the T/R attach cone on the boom so the tail rotor can have an upward thrust as well as a sideways thrust, this will, I Hope go some way to reducing the need for the ballast weight as there can be an upward thrust on the boom making it more level in a hover, this will need to be tested. I will be spinning the tail rotor itself slightly higher rpm as well so a little more thrust as well.