Few things... First your ready. Sign up for one now and that will give you the motivation. It works.

1) A HIM swim is something like 1900m right? An olympic is 1500m. There is not much difference here. The difference in Olympic and HIM is not in the swim, its on the bike and run. How is your swimming coming for the oly?

2) Frankly you run too much for HIM training. You need to significanly increase your cycling. This is a universal truth.... cycling helps running, much more than running helps cycling.... The key to long distance tris is cycling. It is all about the bike. I do IM, I'm doing 3 IMs this year and I run at most 4 days a week. But I cycle 6-10 hours a week. And you know what? I run faster than I ever did, in fact I'm looking to go sub 3 in a marathon soon, and just cracked my HM time on a super hilly course by 15 minutes. Cycling is what you need

3) Of course if you increase the cycling, running 13.1 off the bike is cake, but not with how you are training now. You have a runners schedule. You need to convert to a tri schedule.

I would say early next year go for it. Depending on where you live.. you could do Ironman 70.3 in CA in March (or is it April?) You got more than enough in endurance it sounds, just refocus your training, look into some HIM schedules, or get a coach. If you can do the Olympic swim, no problem on HIM swim. The key to doing well is the bike shift.

Good luck.

I thought the same way also coming from a run background.  I had done 10 marathons previously and wanted to get into Ironman.  I quickly found there is a big different in endurance and muscular endurance, which is the ability to push a big gear for an extended amount of time.  You get this training on the bike.  Your endurance from running will certainly help you sustain a long ride (2+ hours), but it doesn't mean you will be going fast on that ride.   I focus on four bike sessions a week, sometimes five, but mostly four in my training.  You may want to do 2-4, but what I would try to get in are the following as priority:

1) Long ride - Try to get something in once a week.  You may want to build time on the bike every three weeks and back off the next.  I would look at some HIM plans to see what they would suggest as the longest long ride.  To me, you couldn't do too much, I would think you would want to get your long ride to maybe 4 hours, even though it may not take you that long in the race.  Over distance is ok here and good, unlike when training for a marathon.

2) Bike technique - These would be mostly done on an indoor training.  You would work on things such as single leg transistions, cadence workouts, etc... Believe it or not there is a lot of technique involved here in cycling.   Its not just about pedaling.  The more efficient you learn to pedal the better your legs will be on the run

3) Bike strength - This would be hill work or a lot of pushing with low cadence in the big chain ring.  Building power essentially

4) Some type of recovery ride outside.  Work on handling.

I'm not a coach so I'm can't say what you should exactly do on each of these.  I suggest you at least do 1 and 2 a week.  I also run or "brick" off my long ride.  You want to get your legs used to running off the long ride.  But the run can be short 10-30 minutes.  All you are doing is triaining your body to get through the transistion from bike to run.  You shouldn't run long off a long bike, save that for race day.

For swimming..... well you just need to get in the pool and get it done.  Until a few years ago, I hadn't swam in 20 years.  I enjoy it a lot now.  However until I took some lessons and got serious about improving my form, I didn't enjoy it that much.  Now its very enjoyable.  Its great for the body also.  Invest in some lessons from a good coach is what I would do first.  Its always good to have someone take a look at your form and to help out.   Swim is a sport you need to do 2-3 times a week at least.  I only go 3 times a week to the pool at most, but I also do some "dry-land" strength training that is swim specific.  If masters swim is available, you may want to look into that.  At least you would be swimming in a group, which I find much more interesting than going alone.

You've got lots of info from others..  If you want some training plans that you buy 1 time and that will serve you well over the long haul,

I recommend the Matt Fitzgerald book--  http://www.amazon.com/Triathlete-Magazines-Essential-Week-Training/dp/0446696765

You'll also find each of the book plans are used in the Training Peaks website, http://www.trainingpeaks.com/cuttingedge/

but you get "EVERY" plan in that one book -- by itself.

So you can decide what level to work at -- from relative newcomer with little time to hammerhead willing to work out 4 times a week in each discipline.

-  and yes, you do need to get swimming and especially cycling to do triathlons. If you're not willing to do that, then they have a term for those people --- " runner".

Even the most hardcore tri program will cut your runs to 4 days a week.... but that's with also doing 4 bike days and 4 swim days.

Think of it this way -- at almost every fitness level, the cycling time in a triathlon is usually around 2-3  times that of the run times.

(simple examples: IM winner last Oct --  swim 51:48, bike 4:37:32, run 2:42:02    &   70.3 winner last Nov -- swim 22:57,  bike 2:04:29,  run 1:11:33   )

Beware looking at these champion caliber swim times as well. The average novice (non-swim team background) isn't going to be anywhere near

1:30 per 100 meters, as these people were.