Jeep,
What size Super Cub. BUSA (1/3), Sig 1/5, Horizon, Great Plans/Tower, Dyna Flight and now Dave Patrick (1/4). You say you have the Sig J-3, why not get another and bash it into a PA-18/L-21 Super Cub. The May 1998 issue of RCM has plans (#1251) for a 71" PA-18 with Edo style floats (can be built either way. Flying Scale Models (British magazine) has a 79" (1/5.33) scale plans.
I had taken the RCM plans, enlarged them to 84", bought the wood, wheels (Dubro 1/5 Cub), Robart landing gear, cut out the ribs and half ribs and then Sig came out with their 1/5 J-3. I will use the RCM plans to convert the J-3 to a PA-18. Differences are minor (flaps, one piece wing vs plug in, cowl and some other things). I plan on using servos in each wing for the airlerons and flaps, possibly putting Trexler #11 tires on the Dubro hubs for the big bush tire look (duability question) and maybe putting Horner style wing tips on.
Sources - Cub Crafters (wide body fus, square dash) Dakota Cub Aircraft (droop flaps/airlerons, slotted wing, Horner tips) and Bob Banka for photo paks. Do a search, there are many sources for scale info and model kits and/or plans.
Just decide on the size you want, gather the plans, wood and/or kit/ARF and go for it. If you need links for sources let me know and I'll get them to you. Good Luck