Hi Jack!
Indeed this is just where 1/8 of my ancestry comes from. Forest of Dean area is certainly relevant. My “other” names in the vicinity are George (Llanishen, Mons and St Briavels), Hanbury (Mons), and all too many Jones, Lewis etc (nothing against these noble names, they are just untraceable for me in this region). Which towns of the area are your Harris from?
The Harris line of Welsh Newton securely begins with a John Harris, who died in 1820. He has three sons (John, Edward and William). These three were born in WN in the first decade of the 1800s, mother was Mary James. I descend from Edward who married an Ann Lewis. William married a Catherine Jayne and moved the US. I have dna matches with several of his descendants. I just found that Edward makes a (minor) appearance in the National Archives: he was a Royal Marine from 1832-1840 recruited by a Captain Gillespie.
Have you taken any of the autosomal tests? I match Harris and James (and one Hanbury) on Ancestry.
Frankly the greatest mystery of my tree is Hanbury of Monmouthshire. I have been plugging away at this for years with a number of interesting hints but never any proof!
Cheers, Dave