I've got a similar problem, but I was thinking of using a spare Dura-Ace 7700 9spd (short cage) RD (or its Ultegra counterpart) & 12-25 cassette in back with a 38T Race Face or Wolf Tooth wide-narrow chainring up front. Thinking of using a Dura-Ace 7700 bar-end shifter because I don't want to buy too many parts for this.
I'm not planning on doing any serious racing, but what kind of potential problems will I be running into? Should I consider using a MTB RD? I usually keep MTB and road bike stuff apart, so I don't know how it'll all gel together. How will a MTB RD interact with a bar-end shifter?