The 848 refers to the last three numbers of the serial # found on the top of the head next to the valve cover on the manifold side. I think the last year made was 1959. Its a 8.25 compression head stock and is a good platform to upgrade for the 261. You'll have to drill a steam hole that matches up with the 261.

"Drugs are money, money is power, power is security." - Kent Heiner
Nedrow population 2212
Carbon footprint family of 2/11 tonnes of CO2/yr