Much has been written on "re-riveting" the frame.
The technique seems to revolve most solidly around "closing in the holes" by welding, getting alignment, drilling, and then re-riveting in a fresh hole.
The hole CAN be expanded by the previous riveting process, which makes a new rivet placed in a drilled out hole more questionable. There may be oversize rivets now available to remove the need to weld.
"Rivet Kits" are available which give you the correct size and count of rivets to do a job. IIRC each crossmember has its own kit.
A gas torch with a "pencil head" would be best for heating the rivet shanks. The rivet gun can be any of the air guns commonly used on exhaust pipe splitting work. There are tools made to a standard size to fit most guns, and available at the same Model A supplier who provides the rivets.
As to technique, one is best advised to follow the description in the "How to Restore Your Model A" series of books. The writer of that article even gives dimensions of "dollies" to aid in your re-riveting.
Re-riveting is NOT something you do with the suspension under the car, or the body on top. At least not to do it right. The use of these dollies involves "flipping" the frame and making the approach always from the "top" supported by the dollies. IIRC, he "dimples" the dollies to receive the heads of the rivets in certain instances.
How to Restore Your Model A Jenkins, Bill, "Riveting the Model A Frame", photo, illus., Volume 4, p 4-5
My last inquiry into this (for re-riveting a Model A center crossmember) was back in the near years after 2020 - when rivet supply was a little "challenged." I imagine they are available now. I'll have to check...
Joe K