I've got a spare trigger group in my parts box. Lightly used. $85 shipped. It's the hammer, trigger and disconnect. The original springs will work. I think I've got some spares of the springs as well but need to check.
What do you want the new gas to do? Generally the early barrels (type 0) are over gassed when people have swapped the blocks out. RA used a larger gas port on the early rifles. Most of the guys that went to the finger adjustable block(type 1) ended up having to run it on setting "S". The low profile dial (type 3) was supposed to restrict the gas enough that they could help with the early barrels but I think the type 3 is still on the over gassed side, even on a newer barrel.
You can easily swap out the gas block and the piston head to make the conversion(or a whole new op rod). It may be beneficial to keep the old gas block and op rod as a spare.