Hello - I read this post before walking Hadrians. We were 3 (experienced) scandinavian walkers who did the Bowness - Wallsend in 3 days.
I was surprised at this discussion: 84 miles breaks down to 28 hours at 3 miles/hr.
Here is a photoseries from our walk turl.no/1y6f
At 136 km that is three marathon-length days (we did the Waendel walks the weekend before, which is 26 mi/d and the UK IML, 2 days in Wellingborough and then 3 days on Hadrians, altogether 230 km in 5 days walking). imlwalking.org/index.php?page=members/Wellingborough.html
So once you are trained for the 26 mi, it is quite comfortable to do this distance in 3d (10 + 8 + 10 hrs).
(2 x 14 hrs is more arduous - you would have to get up early).
We walked West - East stopping at Haltwhistle, then a shorter day with visit to Vindolanda through the national park, stopping at Chelmsford. Then past Newcastle to Segundum day 3. Also added Wallsend- North sea(10 mi) to complete the coast-to-coast the following morning, did the visitors centre, diplomas etc.