Sorry for the delay I forgot about this until an hour ago
I did this same drop a few years ago. I know I had removed the bed but couldnt remember having any trouble getting in there beside the fuel tank. I went through my old pictures and found that I had removed the fuel tank(single tank). It needed a new sending unit so it made sense to remove it at that time. For you I would suggest either removing the tanks, removing the bed, or possibly getting to the rivets from the inside of the frame rails. I dont remember how much room there is in there.