This. The HTA guns I've seen were registered unmodified receivers that had a custom sear/trip in the lower that works as the conversion device. As a general rule that custom trip has to stay with the gun. Sounds like you have a registered sear in it for some reason as well.
Now with the HTA guns most smiths move the custom sear to ambi lowers but at least one of the ralphs has put 4 position packs on them. I'm not sure if they are moving the old trip and messing with the pack or destroying the old ones and cutting a new pack for the gun. It would be questionable if this is legal.
At 25k though if the sear is stamped in the lower with the serial on the paperwork I'd prob go for it. I wouldn't think it would be an issue to separate it from the upper as its papered as well and even if you end up with what amounts to a sbr(registered as a MG) and a normal transferable sear you are coming out ahead. If you can get an OK to install a new trip in a lower for the transferable receiver than you really come out ahead.
