Well I just tried with both my Axial 28 and my Picco 28, both with PS backplates, and they both fit perfectly...

That suggests that maybe the RTR mounts are just the same.. If the stock - what is it, SH 28? - engine doesn't have a huge backplate like on the Mach, maybe the RTR mounts are just the same as the ones I have now...

I measured about 3mm difference with the MAch, and that spacer is 3,15 mm... Sounds right...

I think I may throw one of my Axials in the Hyper to just try it out in the winter, etc.., and wait to break the Mach in in the spring, so I've got time to find the solution..

I bet the solution is just that plate too...