I guess that only you will know if you can walk/run 60 miles a day for 3 days. If you don't know I guess that the answer is that it is unlikely. Don't underestimate the number of stiles you will have to get over and the time to navigate especially in the dark/rain. Presumably, unless you have someone driving around with food/putting up tents etc, you will be camping as there won't be too many B&Bs that will want to see you. Think about it!
Pennine Way 2005&2014;C2C 2006;SWCP 2007;WHW 2008;GGW 2008; Dales Way 2011;Clev.W 2012;Yorkshire W.W. 2012;Offa's Dyke 2013;Peddars Way & Norfolk Coast Path 2014;Pembrokeshire Coast Path 2015;LEJoG 2018;Camino 2019;2020 NOTHING!2021 Hopefully.