This system IS STC’d for the 108 series aircraft. https://betteraircraftfabric.com
I’ve always wondered what makes the small tail and big tail frames different. I compared the drawings from the general service manual. In general, everything in pink is a little bigger tube and/or slightly thicker. There’s a tube across the tail that’s removed going to the -3 and battery box tubing support under pilot seat removed and tube added to firewall area where battery sits on -3. Curiosity peaked my interest.
I was a little surprised on the areas. I figured above cockpit, but was wrong. I’d almost think if you did the work in the cockpit area and slapped on -3 wings (because of the different spar alloy), one could attempt to up gross a small tail another 170 lbs to 2400 lbs. I assume the tail members are for the bigger tail so may not be required. I’m not an engineer so I don’t know. Just what I thought looking at it.