Surfing Waves

Hey, folks. Looking for help. I have an 8'6" that I use pretty much as a longboard (I'm 5'0" and 90#). It currently has the FCS G5 fins it came with (which in the FCS catalog are described as shortboard fins). I would like to change up the fins to make it more "longboardy" and a little easier to manevuer, but the center fin spot has plugs, not a fin box, and I'm not finding a lot out there. I'm wondering what my options are. I broke one of my side fins off this morning, so am in the market for new fins anyway, and figured this might be a good time to try something new.

Thanks!