Engine number decoder

Briefly, nearly all LA Small blocks (68-up) have the information right on the side of the block. The displacement and forge date are cast right into them. You can also look on the left front there is a machined pad just below where the cyl head mounts with cid and additional information on it including the assembly date. The pad information is stamped not cast. They should all work in your car.

the next issue you'll likely have next is transmission torque converter. I assume you have a 66 automatic? early used a small crank hub the later used large. So there might be a miss-match and the internal external balance will also make a difference. these can be made to work by a converter builder, but you need to know whats what.