I would change the wording of Assemble to make sure players know that if the artifact is a creature that the creatures power and toughness add together. Also possibly limit Assemble to creatures that have it. In other words you can't assemble two artifacts that dont have assemble. I hope you can see why this could be a problem. Otherwise I like the way you applied this abandoned mechanic.

The suggestion for the reminder text is a good plan. But it'd be really sad to restrict assembling to only cards that already have assemble. The whole fun of the mechanic comes from squishing together random artifacts from all across Magic's past.

Yes, as Alex explained, the intent was 'squishing together random artifacts'. :D

Also, any suggestions of clear and precise wording that isn't to wordy would be appreciated.