Success!!!
Thanks for the info Max. As you were repsonding I was in the garage tinkering.
I ended up taking the starter assembly off the gxv160 (dual pawl) to see if it would fit. The bolt pattern matched up and after some very minor reshaping of the cowl the cup was spinning without fouling too.
As I went to pull the cord it resisted the recoil and remained extended and slack. I figured that the black plastic drum was just being held up on the metal cup. I jammed a few washers under the 10mm bolts as a 1mm spacer and voila! She pulled over and started up without slipping or fouling.
I now know to get a double pawl gxv160 starter assembly and away I go!
After mowing the front lawn with excitement I've now decided that the chassis of the Honda is far better than the Rover chassis the gxv160 is sitting on. As such, I'll swap the 160 onto the Honda chassis and find a 19inch victa or similar for the hru194. The rover chassis is just too cumbersome and needs new bearings for the wheels.
Overall; success.
