I'm pretty sure you have the u-clip retainers. They had them on the 64 Merc for sure.
NAPA (Canada) UltraPro #60371
Handle Removal Tool, Removes Spring Clips
If you have trouble finding this style of tool, you could do what we did 35 years ago ... improvise! (We were living in the middle of nowhere!)
I used a hacksaw blade, ground all the teeth off of it so that it slid through without marking the panel. I used tin snips to cut a "v" notch in the side of the blade to the mounting hole, and then bent the resulting hook slightly sideways. I then slid it in from the head end of the clip, hooked it, and pulled it off.