Not sure if you thought of this already, but the bore and stroke are different between 12 and 14-hp engines. A simple measurement of the cylinder should tell you which you have. Easy to do with the head already off. If it's all bolted up, there's basically no way to tell.
1951 Farmall Cub, Cub Cadets 102, 104, 1811, 1864, Simplicity Legacy XL 4x4 Diesel with FEL, 60" mower, 50" Tiller