I just finished swapping everything over from one Spica block to another (due to a broken head stud) on my '72 Spider.
It had been a while between stripping the engine and reassembly, and there's a boss on the left side of the timing cover (behind the distributor) which doesn't seem to be used.
When I stripped the engine, there was a bolt and nut on the boss. The bolt was holding what appeared to be a broken bracket, but I can't for the life of me figure out what the bracket was. All that was left looked like 3/4 of a washer under the bolt.
(edited picture from mikevalant.com)