I’d say minimum, is 54, I’ll bet most people would run 60’s not really familar with the boat, for the $10 difference I think 60 would probably be my choice.
I have a 1yr old Minnkota power drive 65lb 24 volt with auto pilot 54″ shaft length. On my boat 17′ Lund Pike works great. I really want to sell it to get a vantage.PM if your interested.
Another consideration is with a longer shaft you have to change your mounting angle to keep the head inside the gunnels. (Advised) This may take up more room at the bow which could be an inconvenience when fishing other methods.