You could just buy a nice SST gun and have your 30" barrels and forend fitted to the new gun. You wind up with either a two-barrel set or two guns, one of which is the combo you want. Simpler and probably cheaper than converting the current gun to SST from a donor gun. I have a set of 30" NST barrels fitted to my SST Sporter and it has worked out well.

I am still looking for a nice set of BSS 12ga barrels, 26" with a forend. IF you buy a donor gun to get your trigger, I'm interested in the barrels and f/e.