Re: Bought starcraft boat from auction, unable to determine year or model.
Starcraft sold the boat, typically the dealer sold & installed the motor the buyer picked. Often a buyer supplied an engine they already owned.
You're overthinking this. If you want to run the boat w the 40hp, you can. Until you get it rebuilt & outfitted how you want it & for how you use it, its all guess work.
If when your done, it doesn't get you where your going fast enough or perform as well as you'd like, replace the OB.
Who knows, you, the Admiral & 2 kids might be a lighter load then just me & my wife. So my perception of how a 40 will perform is based on info that doesn't match you & your situation.
Sig just splashed a similar size boat, with a 75hp OB. It had plenty of get up & go, got up on plane & performed well. It might be a slightly different hull then yours but not enough to plane or not plane based on the hull alone.