Hi Redjeep, keeping fit during the injury is encouraging.
I've only run one marathon so far (in the midst of training for my second) so my inexperience may colour my opinion, but you really ahve to respect the marathon distance. I'd run quite a few Halfs prior to my first marathon (and spent a few years running shorter distance) so wasn't too worried about the change in distance. I'd enjoyed the leap from 10k to HM, so how hard could it be? Long story short - I really suffered in the full event despite having a very successful training campaign (HM PB etc) as I really underestimated how hard those last few miles would be.
You sound like a self-motivated person as you've kept your fitness,so I understand the desire to jump to full distance. However, I also suspect you'd be your own harshest critic if you didn't give your best in the full distance?
PS part of the "respect the marathon" bit is also that there's no shortcut to the endurance required. You need 5x long runs of around 20 miles plus a couple of weeks taper prior to the event (as the long miles mean you will be tired). If you try and cram that all into eight weeks (as you said, you'll need a couple of weeks before pushing the distance) you're almost cetain to injure yourself.