As others have mentioned, get the HIN. My initial thought in that length and with that motor is a Formula. The HIN will tell you manufacturer and year. From there you can go with length and narrow it down to probably just a couple of models. The fact that it is a closed bow, with the hin and a little research, it should get you what you need.
Just out of curiosity, why do you 'need' to know the manufacturer? What are you trying to do with the boat? as others have mentioned, if you are trying to restore it or make it usable again, start by proper supports underneath. I give it until spring and open to the elements, that 6x6 will have a nice indent made in that hull, if not thru the hull completely.