Most original antennas were usually mounted on the right front fender & depending on who installed it & where & customer preference could be mounted on the rear quarter on either side. IF it is a universal antenna the part that holds onto the fender flexes & you just get the "Fingers" up to where it van be removed.
it would be helpful if you attach pics of what you are mentioning. there is assortment of tools to use in hard-to-reach places. long needle nose pliers, flexible claw, tape, etc. you could loosen up or remove bolt on the fender at the bottom to pull it away to get in there a bit more. not too much just a bit.