That other piece is the overtravel limiter.
You can mill the right side of the Tapco disconnector down and make it work, or just go with the stock Tapco.
If you try to re-use it, fit it properly so everything moves freely, and you have decent disconnector engagement, because the tip of Tapco disconnectors will eventually wear down a touch after several thousand rounds of powerful ammo, and if it's not good engagement to begin with, when it wears down, eventually the hammer will not be caught and will follow the carrier, bolt, and FP back up into battery..... Not. Good. and I've seen some who really should know better screw up on that aspect.
That being said, in the V-12, you really need to profile the Tapco Hammer down to .0555" when measured perpendicular to the hammer face with calipers over the "O" in the word Tapco, which is molded onto the side of the hammer.
(I didn't touch on the bump, or axis length, as those aspects should, by now be common knowledge, but just for shits & grins... No front bump, and hammer axis at 1.01" for accommodation of the V-12's LRBHO)
God bless, & good luck.