Folks,

Back 12 years ago, when I had very limited tools, I put together an AMD-63 screw build.

There was a problem with the left-hand rail being welded in about 1/16th too low and the bolt never rotated properly on the recoil stroke.

Fast forward 12 years.  I have a metal lathe, vertical mill, and generally more knowledge about assembly.  I tore the screw build down, bought a new receiver and rails.

Before I redo this as a screw build without the rail problem, I want to ask about reverting to a rivet build.

Most of the trunion holes are 10-32 threaded but I did the bottom most front trunion screws in 1/4x??

What options, if any, do I have for returning this kit to rivets?

Would I need to drill out the trunion threaded holes and use larger press rivets?  Or would the press-fit rivets hold in the threads?

Any input is appreciated.

Definitely possible.  Sounds like you have the tools and skill.  I have put together riveted ones with less.  Surely others have remade screw builds with rivets, but you may need thicker (shaft-wise) rivets than the original ones, so I would not buy a rivet kit until you know if you need different rivets.  Take time to gather the info...sorry I'm not sure but it seems the threading will need to be drilled out.

Yes it can be done. No you don't need to drill out the threads before squeezing rivets in those holes but you will need thicker rivets than the normal ones. Here is a link to where you may find some rivets the size you need.
https://www.mcmaster.com/#rivets/=162jhxs

make sure you have grade 8 bolts and then clean the threads, mix up some jbweld as thread locker and bolt it back together.