My generator mounts on my '62 are up the side of the block a little ways, where there are two bosses cast and drilled. They are not down low on the flange like 216 blocks were. Did you look up there? It had to be somewhere. I used the original generator brackets to mount my alternator, and that's a good way to do it. It came out perfectly lined up. I'd take a picture but I would have to take out the oil filter and alternator for you to see it.
If you pull up the 261 article and look at one of the pictures on the bottom you can barely see one. It's the two bosses along the thin webbing on the front of the drivers side block. Are there pipe plugs in there or something?

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