RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
that's a raised casting number.
better to take a pic of the machine .. showing left side and post it along with the hand stamped number ont he left back side of the block, aft of the oil filter on a flattened 1x4 boss.
RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
they are hand stamped super light to begin with.. many times there may only be faint traces. occasionally you get a repalcement block with no numbers..n npic fromt he side will help id it based on installed options