It looks like a 67 or newer 273 2 barrel according to the valve covers. Pull a cover off. Up to and including 67, 273's had a solid lifter cam and adjustable rockers. 68 and 69's had a hydraulic cam and stamp steel non adjustable rockers. Look around for casting dates on the block. Depending on what you want to do with it it really doesn't matter what it is. The transmission looks like a 727 and 66 or newer because of the slip yoke tailshaft.