Hi Mark, it is possible to train up to doing a marathon in the time you have. However, that said.....I would take things slower if i was you, esp as you seem to have an injury. For the marathon training, you would have to be covering at least 20 miles a week and that would only ensure you get round. For example the training program i am currently doing, has me doing between 30 and 40 miles a week at the moment. Why dont you get your self a training program for the HM your doing and see how that goes and then perhaps a week afterwards have a think about whether or not your ready / have the time to train up to and run twice that distance.
If is was me, i propably wouldnt do, but like i said if you really pushed yourself you could do it, everybody is different.
Edited: 23/08/2012 at 10:00