It won't be possible to make it fit inside a stock gearbox housing whilst using a large, modern slipper pad. It can be made to use a .6 module, however the availability of larger pinions is very limited and the largest I've been able to find is a 25t. Going to 48p would allow a much larger range of gearing options.
I envisage a drop in replacement gearbox, that will appear stock on the outide except for the adjustment nut for the slipper. Much like other Tamiya aftermarket options for example the stealth gearbox drop in for an astute/Kingcab platform. Or like someone recently designed, a gearbox for the Astute that takes Schumacher gearing and slipper, due to the limited availability of the TTC gearbox and the fragile nature of the stock box when using modern more powerful Brushless setups.
Presision did a spring loaded spur for the FF01 and the TA01-02, I have both, however, the spring isn't that strong.
HPI also did a very small slipper for their RS4 range that went on the layshaft and allowed it to operate on one single belt.
i did look at trying to design a drop in replacement spur, but there just isn't the room available.