http://www.inliners.org/
There's a very good casting # list on this site.
I cab tell just from the shape of the rocker cover (scalloped on the left) and the distributer location (towards front of the block) that it's not a 235/261 (squared off rocker cover and dizzy is centered on the block). Like I say, I come up with 292 from the serial # (SCORE!! ) but it wouldn't hurt to check another source, just be certain. Perhaps someone more versed in the later 6 can give you more info.

Bill Burmeister