I picked up a 261 block yesterday and was surprised when I decoded it. I'm pretty sure that they were available in 2WD trucks until 1962 and 4WD (K series) until 1963. I've also heard that GM made replacement blocks through 1964.
The one I picked up yesterday decodes to a December 6, 1966 casting date with L66 stamped on the block. The casting code is 3769925. It has the dowel for the oil filter consistent with 1959 and later 261's, so I know the last 6 in the date code does not stand for 1956. There is no serial number on the flat by the distributor, indicating a replacement block.
Pictures attached.
http://s844.photobucket.com/user/ma...2443_zps1ecpla6u.jpg.html?sort=3&o=2Sharing for a couple reasons that I thought others might find interesting. One is the late date code, much later than the final 1964 casting date that has been previously reported on Stovebolt. Second, notice the clock that is cast into the block by the date code. From what I have researched, GM began to add these to identify not only the assembly conveyor and the date, but the shift and hour of the casting. Never seen the clock on a 'bolt before.
The engine is locked up. It sat open to the elements for many years with the head removed. I hope to be able to save it, but I'm not sure about this one. Even though I live in the dry Arizona desert, we do get a little rain. After I blew all the desert sand out of the open cylinders, I wire brushed the tops of the two high pistons. They are marked .060 over, so there isn't much room left on this one if the rust is very deep. It is sitting in a corner of the garage with Marvel Mystery Oil poured into the cylinders. Fingers crossed...
Matt
