Is there a good way to remove the spot welded reinforcement plate from a demilled underfolder receiver without destroying it? I don’t have access to a mill.  I’m thinking of taking a torch to it and then chiseling it free. Any suggestions that have worked for you will be appreciated. Thanks.

Use a carbide burr/rotary file in a drill press to remove the spot weld.   Use one only slightly larger than the spot weld that has a flat cutting face like an end mill.

Excellent! Thank you.

or.......

https://tinyurl.com/23b6o3no

Hey guys. Thanks again for the great suggestions. I'm glad I asked here first instead of taking a torch to it and probably butchering the thing. I ended up going with JKH62's method because it was the cheapest. I think the tool was around 6 bucks at HF.

Here's what I learned: You don't have to cut all the way through the old receiver for this to work well. In fact, just stop a little short to avoid cutting into the plate like I did on my first attempt. Creating a dimple with a center drill countersink first will save you from the tool walking. Bend the sides of the old receiver outward to avoid touching the tool to the side of the receiver. I didn't initially and it immediately broke the teeth on the tool. Once you hit every spot weld, a thin steel paint scraper can be worked between the plate and the old receiver. It only took a few gentle taps with a rubber mallet to separate the two pieces. No prying. Then I took it over to the bench grinder to remove what was left of the welds to get the surface flat. A flat hand file would work just fine, too.

I hope this helps the next guy doing this. Thanks.