I'm guesstimating that I'd probably do this run in the 3 1/2 to 4 hour bracket.
What do you think is a reasonable first effort - I run 35 to 40 miles most weeks all off road in the dales and lakes and would reckon to do the Wharfedale off road marathon in say 4 or so hours. I've run the 3 peaks of yorshire half a dozen times (3 in the proper fell face) with a PB of 4:40 ish but I have been doing much more running of late and (touch wood) don't have any injuries so maybe a 4:30 better fits my current 'speed' ...... if speed is the right word