Tlh
Hello & Welcome to the Forum!

Many of us in the process of restoring old rolling stock have encountered the same problem. true some of the epoxies/adhesives available today will work, but is nice to just be able to spot weld things together.
I have come across an article that suggests using a lionel 1044(been years since i read th article) I used the little blue box L. transformer I had..  make contact points out of stainless wire, affixed to a clothes pin.  connect to the outputs on the L. transformer. when the wires meet, you get a small spot weld.  You should be able to napkin engineer the spot welder.

I'll see if I can locate the article and repost it here.

Happy Rails!
dave