Stainless steel and aluminum will corrode over time as they are two different metals that will corrode. However, that will occur over time. I have seen the stainless steel pop rivets used vs. aluminum pop rivets but the strength is in the stainless steel. The big concern was on the outside for the corrosion to occur which did occur over time not so much a worry inside the mast. I use to drill the holes and would place a sheet of rubber or neophrene between the mast foot and the stainless steel pop rivet and then attach it which was good so the two metals would not touch on the outside of the mast. Then cut the access rubber sheet or neophrene off. Not an issue but you have to use a thicker piece vs. paper sheet size thickness.
Pop rivet guns you buy are very difficult to install the stainless steel pop rivet guns. They use to be expensive but years ago after mine had been stolen, I purchased another big pop rivet gun at an automotive store and the cost had come down substantially.
As for using the original mast holes as long as they are not torn out, that is fine. If the poop rivets tore out, simply drill in a different place which you will be fine. Many think of a lot of forces being applied but in reality, not so true which some will disagree but too long to go into an explanation here. However if the mast is ripped up to the pop rivets, simply cut off that 1 inch or a little more but the issue would be the rigging at this point. In most cases, that was fine but more of the studs in the turnbuckles. You would have to look at the cost of the shrouds of shortening them vs. a new mast and so forth.
If the mast is fractured or ripped too far, I always said time for a new mast and when folks talk of sleeving the mast that cannot happen as you have to have a piece that will fit exactly inside the mast for that and it was never made for an inside sleeve by the mfg. For those who say weld a mast, I refused to be a part of that as too many forces are exerted and I have seen the aftermath of welded small boat mast.
