Normally for that style of gooseneck there would be a short section a few inches above the gooseneck's normal height where the flanges on either side of the mast track would have been cut away. This gives you a spot to feed the sail's boltrope into the mast track as you raise the sail. Then the gooseneck is fed into the track and drops down below the cut-out to proper boom height. The pin through the big shackle on top of the gooseneck secures the sail's tack grommet and a downhaul of some sort attaches to the hole on the lower part of the gooseneck.
Downhauls can be fixed, with little more than a rope attached through the hole and cleated off on the lower mast, or they can be adjustable, even sometimes with multi-part tackles and a quick release/adjust cleat for adjustment on the fly as needed. They can also be set up to float with mainsheet tension. In that case, a mainsheet block would dangle on a shackle from the hole in the gooseneck, just aft of the mast. The sheet in that case is usually routed from the stern, up to the aft part of the boom, forward along the boom to the gooseneck block, and finally down to a fixed block on the hull below. Sheeting the sail in hard (as you would do for upwind work) would pull the boom and gooseneck downward, tightening the luff, flattening the sail and moving draft forward for better upwind performance. Easing the sheet tension to sail a course farther off the wind would reduce downhaul tension on the boom a bit and allow for a fuller sail. I don't know what sort of fixed or floating downhaul Old Town had rigged on their Class C rigs.
Also know that your gooseneck is designed for a sail with almost no tack setback (the distance between the aft side of the mast and the sail's tack grommet when the sail's boltrope is in the sail track). It is important that when rigged, the grommet is in the proper spot in relation to the gooseneck and is not distorting the sail's corner. If the sail and boom/gooseneck were made for each other, then it shouldn't be a problem. If they were not, then it can be. Likewise, most oval masts will use a small cast aluminum cap at the top with either a sheave for the halyard or a hole for a shackle to hang a halyard block up there. Again, you want that assembly to line up well with the peak grommet or headboard grommet on the top of the sail. It's pretty straight-forward. If the sail in that area is creased, wrinkled or seems to be being pulled funny from the halyard, something isn't lined up properly.
