I took the plate off the bottom and adjusted a nut on a rod on the bottom of the Box.This gave me more "reverse gear" I simply screwed in inwards,along the shaft.this moved the forward/reverse lever further back.
The shaft is cross drilled and the nut castleted ,so if you go past the factory hole for the split pin,you have to lock it with another nut screwed ontop of it.
This has so far sorted my problem of it hoping out of reverse.The larger gear felt a bit sharp on the edges,but I think that was a result of the selector not picking it up correctly.Its a simple fix,took longer for all the Oil to drain than to do the job.