I've had the idea in mind for years, I think a -4/-6/-7/-9 would make a fine ski plane. Limiting cables could be attached to lower engine mount bolts and rear spar attach points. Wheel penetration or wheel replacement skis could be used. Would involve some flight testing and likely a reduced Vne to keep load on rear spar attach to a minimum. Additionally it would involve a change in operating limitations and likely a Phase 1 test period. My big concern is the added stress placed on the rear spar attach fittings.. there are some ski setups that don't use limiting cables but rather a shock absorber/limiting system, this would solve the cable issue. Either way it would be one FAST skiplane!