On that style of ID plate, I don’t believe the rivet holes go all the way through the bracket so you can’t get at them from the underside. They are in fact drive screws (like a rivet with coarse threads). You might be able to carefully get a thin blade screwdriver up under the head of the screw and pry it up just slightly, then grab onto the head with pliers or vise grips and remove it by turning it counter clockwise. If not, you would have to drill them out – hard to do on such a small diameter fastener.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
1982 Evinrude 25hp
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."
