If your longer shelves do actually fit the pins, I would cut out the middle and epoxy some pieces at least on the bottom of where you cut out the extra. Perhaps drill some flat head screws through into the new piece to ensure they don't break in half under load.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel