Somethings not right there's no 704th day of 1970, all the 850's i've seen the part number and manufacture date were on the front of the carburetor on the airhorn if it wasn't milled off.
Ah, I see the 4781 is on the metering block... strange. Should be on the front air horn which looks to be milled off by that pic? If it is the carb isn’t worth much at all.
Guy, good Eye usually the chock is removed also. Hard to tell with the chock still installed in the pic. It's just a basic modified 850 now.