Along with so many other parts on these bikes the 85/86 FX frame was a limited production run and is a hybrid of the shovel and softail frame. You can´t fit an earlier shovel seat because the mounting at the front is different and the FXDWG is completely different frame so later seats won´t fit either. I bought a Corbin Gunfighter and Lady but found that it only really suits a mid-shift riding position as it puts the rider further forward than the standard seat. The alternative solo saddle might be an option. I finally got my original seat customized and re-covered to look like a Corbin for about £60.00.