On my 2nd marathon London in 2007 (3.00.13) got overtaken in the last 800 metres by a load of guys chasing the sub-3 pacer who were debut marathoners and they sub 3 (o how I hated them!) so it certainly possible.
If you hit the following milestones, you increase your chances:
Aim to run faster maybe a half marathon time of 1.24-1.25
Build endurance - At least 4 runs in training of 20m plus and make 2 of these progressive, i.e.faster second half than first.
50 mpw, the more the better as long as you don't cross the getting injured line
Lots of sleep and recovery
Then a fast course on a cool day - April in Manchester must give you that.
TJ - Also a newbie and just done Gower Olympic on Saturday - me: good runner, ok cyclist, below average swimmer - and looking at the Cotswold 113 / Classic events in summer 2017. Offers a lake swim and flat bike and run so should be 'easier' than most.
Injured with calf tear through Feb, overdid the training in the first 2 weeks of March so got very painful shin splits for the first time and off the road for the next 10 days. Returned and did the VLM on Saturday with the pain free return thanks to taping (see youtube on how to do it), gentle massage, icing the painful bit and running in compression sleeves. Shave the injured bit for the taping and massage, Good luck.
I am impressed. Rest and cross train well and I look forward to hearing how you did, and how you found Prague, on my (long) list of marathons to run. Injury and tapering is an issue of interest to me as I've missed 6 weeks of training for the London marathon since February all the long runs!. The cross training (I hope)has really helped.