You can check the old handrails and see if you can make out round bungs where the bolts may be. Look very closely for a round circle in the teak.
If you find one, try drilling the teak bung out, or drive a screw into it, and it might pop out when you hit the bolt head.
From there, if you can unscrew the screw, you may be luck, and you just back out the screws.
On my 1988 O’Day 322, the teak handrails are thru-bolted. Same teak bungs on the outside, but inside (I have a hard liner with holes in it for each bolt.
If thru-bolted, you will have to remove the liner somehow…and get a wrench on the nut.
Greg