I have been doing this on my a frame. Someone had ground or cut off the rivets on the outside to remove the running board brackets. So step one would be to grind the head off of one side flat with the frame. Step two is to take a coal chisel to the head on the other side that is still in place. Just get under it to loosen it a bit. You'll see on the outside it is starting to come out. Step three is take a bfh and a punch and knock the rivet out from the outside. Wear gloves in case you miss with the hammer.
Cut the head off, drill hole thru center,1/2 diameter of rivet and than hammer and center punch out or pneumatic if you have
I like to drill first, then grind. It doubles the work, but I lose sight of the rivet when I grind it flush with the surrounding metal. This way I know the drill is centered in the rivet itself and not off a little bit.
I drilled mine, then knocked the head off, followed with a center punch. Worked great and not a mark on the frame. New rivets went in and look as if they were factory installed.
use a cuttoff wheel, make an 'X' on the head of the rivet, hit it with a punch and it'll pop right out.
I like a cutting torch.Small tip. Cut the head off (ok if some left over) Now the rivet is red hot,correct size punch and one hit with BFH Playing with fire is fun.
I prefer drilling the head off then drilling the rest as well if the rivet doesn't come out with a puch. Hammering to hard tends to cave the area. Or at least have a buddy hold a heavy weight from underneath near the rivet. Some of those rivets are realy in there.
Grind the head flush to the frame then gently hit around the area with a hammer and the rivet outline will show up,hammer and punch it out.
I use an air hammer with a flat chisel bit to cut the head off, and then just switch to a punch bit and push it through.
Its easy to do, and the previous posts offer good advice on how to do it. I have rebuilt four 33-34 frames by taking them completely apart - that means removing all the rivets. The various pieces are then sandblasted and using the holes left by the departed rivets, are bolted together. Once everything is square, the frame can be welded together. I try to duplicate the rivets by filling the weld holes and leaving a little mound on top - once the paint is on, it does look like a rivet. I recommend welding more contact areas than the rivet holes though to keep the frame completely strong.