Back to the drawing board - Spoke to the local All Terrain and Mower store (as they are the local Victa dealers) His advise is that the VEX160 two stroke (largest available and on the Victa Slasher) would not be powerful enough to drive a self propelled (the Victa slasher is a push job) He recommends a pressure fed 4 stroke as most of the larger engine are now days. He puts them on their all terrain mowers and does not have any problems on steep slopes. A splash fed would not work on a slope - as I found out. So the GXV390 looks the goods as he advised at least 8HP for self propelled.
