position modern(80/20) keel fins

good morning swaylokiens, i’m working on a sandwich semi retro fish and prepared it for a quad (rear 6 1/2 from tail, 1 1/2 from edge, 2 outside nose) set up. now the guy send me a mail and ask for a 3. fcs plug, he wants to use fcs keels (modern 80/20 foil). what would be the position for keels i’m afraid that the keels would need a complete new position instead of just putting on more plug in front of the rear quad pos…

i have never owned a retro and never done one so every input is appreciated.

thanks

uzzi