I bought a 1990 20' Pontoon with same year 40 hp Johnson VRO (disconnected) I'm looking to replace Impeller and rebuild cards. Thing is, on the impeller for the 40 hp they have listed for the both brands 2 impellers. A 40 comm (I'll assume that means commercial) and then just a 40. How do I tell if my motor is Commercial?? And while we're at it, which brand would you recommend on the impeller and carb kit, Mallory or Sierra? Thanks.