[FFR428]

If the block has core plugs on the front (2) and rear (4) of the block (like the three on each side) it's a late 50's block. I think these were dropped in 60 just using the three core plugs on each side. I've e mailed a bud of mine who should be able to help as well. I'm not sure about the dots skipping a decade either but anything is possible. I'll forward any info I can asap. G.