I had to miss Edinburgh last year due to illness and I got a last minute place at the Kent road runner marathon. I think it's at the start of June this year, they might still have places. It is multi lap and there is a hill in the lap but it's not hilly as such. The organisers do their best to make sure it's a really good race and it's so small that there is no congestion on the course.
It depends on how good your swimming is and cycling is. Don't think that you can wing an IM though. You were lucky today and are obviously are a decent natural runner, but you need to put the miles in on the bike to do an IM. I spent years building up to IM, but the actual training was about 5/6 months.
Btw, just re-reading your OP, mine is also a dull ache, just letting me know that it's there and I dont like it! A dull ache to me = a reminder that if did too much, it would get worse/something isn't right. I just want it to go away. Previously my knees (unlike most other areas of my body) have been fine.
I am in a similar position. I was knocked off my bike (by a dog, 6 weeks before London!) and I also did some knee damage. I also had an MRI, knee specialist etc. I cant remember what the exact diagnosis was but it was a bruised knee, a few other things but no ligament damage or anything serious. The specialist said that it should take about 12 weeks to get better (this was 5 weeks after the accident) and in that time, impact would not be my friend. He said cycling and swimming would be though. I cycled a few weeks ago and it was a little swollen after so i left it and am trying 7 miles tonight and seeing how it goes.
I'm not sure if I am helping, but having withdrawn from London and really taking a step back, I am really nervous about starting again. It never really hurts when I do stuff, but i can feel something. As with you, I am more bothered about having a functioning long term knee than any race, but I do want to do Abingdon marathon on Oct 20th. My physio seems to think that will be fine.
In the meantime, my physio have me doing work to try and strengthen my quads and glutes, without putting pressure on my knee. I am doing
- bouncing on a 75cm swiss ball holding the upward bounce at the top every 2 bounces
- very gentle squats, keeping the movement in the upper area
- side raises, lying on the floor raising my leg (works glutes and upper legs)