While it's possible you have a random failure, it's most likely that the work you did is the cause. Time to look at everything you touched, moved, or could have..
When the trans comes out, it's possible for the engine to tilt and the distributor to hit the firewall. If that happens, several terrible things could result, or maybe nothing would result.
But I've seen shafts snap, caps come loose, wires come loose or get pinched. Also possible to lose a ground strap and cause the ignition to not fire. It's also possible the bulkhead connector got rubbed, bumped, or otherwise disturbed.
Hell, I've seen main battery cables get pinched when putting in a trans. Reconnecting the battery caused all kinds of fireworks..
I'd start with making sure the distributor turns when you crank, and that you have a good ground to the block. The fact you have no headlights is also a clue that it could be a ground issue. Don't discount the chance that old work came loose while monkeying with the trans..