Re: merc 850 lower unit
It might bolt up (sorta) but the shift shafts and reverse lockout mechanisms won't match and there is no provision for an exhaust tube in the older lower unit. I'm assuming your older "850" is closer to '63 or so rather than '60 since otherwise it wouldn't be an FGS (Full Gear Shift) model.
Conversely, you could adapt the newer lower unit to the older Inline F.G.S. motor, but that's a Goose of another flavor!
Cheers...........ed
