The running calculators out there would put your marathon potential (based on your 1/2 time) just a minute or a few over the 3:40 time. That assumes, of course, that your adequately prepared, physically and mentally, for the distance.

In addition to pure conditioning, you've also got to be ready for both mental fatigue and for glycogen depletion at a level you won't experience running only 14 miles. So, while I think you're certainly talented enough to qualify, a smart plan might be to get a marathon under your belt with no intention of qualifying and use that experience to help you chart a plan to BQ. Given your 1/2 times, you should be able to make a serious run at BQ not too many races after (perhaps even the 2nd if you're very fit).