It looks like I was wrong about having the correctly-sized timing chain in my box of parts. The timing chain I have is still too short. Looks like I'll have to head to the auto-parts store and throw down some money on one. Bleah.

In hindsight, it's probably a good idea to buy a new timing chain anyway. While they rarely break, I suppose that having a timing chain stretch too much from 30+ years of use could be an issue.