original equipment VHF antenna mounts on the top of the masthead with the coax and connector protected, or does it mount on the side of the mast?
Unlike automakers with a radio in every car, boat builders give you a sailboat. Radios are dealer options or owner installs. Your OEM could be on the mast or on a pole at the stern.
Attached to the side of the mast was the easiest method. A bracket screwed onto the mast, a hole drilled through the thin aluminum, some amalgamating tape wrapped around the wires & connections your done.
Drilling a hole through the cast aluminum mast head was more difficult and presented a failure point (antenna break’s how you going to fix it, short of dropping the mast).
There is nothing preventing an owner from doing his own thing.