It may be "doable" to be honest I'm not 100% sure. Coming from an aircraft maintenance
background I cringe when ever the wrong part is used for a job unless its an emergency
I know space on your boat
may be at a premium but honestly whats a quart or two. Think about how much you just spent on your brand new engine. Do you really want to risk it over some space, convenience, and a few dollars.
Maybe someone else has some more technical info but remember the manufacturer put those specs on there for a very good reason.