Thanks Bosswrench. I must say I did have exactly that concern and hence the safety wiring. I tried making the collars up from 3/4 inch stainless steel strapping with bent up return bolt tabs but the strapping was a bit light to get the proper tension around the motor as the bolt tabs just bent in ( and it looked ordinary ) , hence had to revert to the worm screw clamps. Not my ideal but they seem to work ok.
The motors are rock solid as they are fully captive between the front support and two side rails on the base. The fan tip to top shroud clearance and bottom grill clearance is quite close - perhaps 1/4 inch ? I was surprised how tight it all was.
I think there are only three Panteras in WA , so If their mounts disappear they would know who did it!