Dick,
On my 59, I'm pretty sure there is a plate with two threaded holes to mount the bows triangle (each side). They allow some alignment of the bows triangle. I used allen head counter sunk fine thread screws, because they are black and can be tightened (tight) without marking the paint. Also I installed the forward screw first, and tightened it to keep the plate properly positioned (with the covered fiber board in place) before installing the rear screw through the bows. That way, it's possible to find the threaded hole when installing the bows (rear screw only). Then I removed the front screw, and used the rear to rotate the plate into position for the front one to go through the bows. When they are both installed, you can position/center both sides before tightening.
Also, it is important to have the bows positioned properly, as well as the triangle positioned properly before attempting to install the top. You want to be sure the bows will go up and down.