Where ya gonna find another new 1977 Evinrude motor? Demanding a new one most likely isn't gonna get anywhere.
It's fixable. Finding the parts to fix it is the issue on an older motor. That and the amount of money it would take to fix. Figure in some labor + parts and then you're into what the insurance company would most likely consider a total loss, based on the age of the motor. But that's not necessarily a bad deal.
You "could" let them total it, then buy it back from the insurance company if they'll allow you to. Usually dirt cheap. Then either fix it or sell it for parts, your call since it's your motor at that point. If they total it and you let them keep it, they're going to sell it for scrap (due to it's age). It's not got much value. IF they total it, they'll cut you a check for it's value-whatever they deem that to be (and that's not what YOU think it's worth, or what it would sell for on the market...insurance companies have a formula for figuring the value). It might only be a couple hundred. Or you might make out great.
then I've had customers who have had similar instances, tore up the foot of the motor only, insurance only paid so much, or they would've totalled it and customer would've had to foot the rest on a new motor. So he took the total loss check then sued the insured for the remainder. And won.