Running a marathon on holiday next week (Read 36 times)

Im off to Guernsey next weekend and have realised the marathon is on whilst Im there, so thought it would be rude not to have a go. The problem is I havent trained for it so am after a bit of pacing advice. I completed marathons in April and May in 3:26 and 3:25. Since then I have been working on 5k/10k and so have not done many long runs - though I managed 20 miles 3 weeks ago and 16 miles last weekend, both around 8 min mile pace. Ultimately I am just doing it for the experience and am not worried about the time, but I dont want to just walk round - I want to give it a decent go based on my current marathon form.  Im confident I can get round and was thinking of aiming for around 3:45. Any advice?