You have to remember that "mild" covers a huge range of beers, that vary significantly between regions and sometimes over quite short periods of time from the same brewery - I know breweries that pretty much had three different recipes for their mild over a period of five years as they adjusted to various restrictions after WWII. Mild was always the poor relation in the 20th century, such that many older Brits would suggest that you can't have an "authentic" mild without 20-30% of slops in it...
To make the point, in the last year or so I've had everything from a Victorian mild from a historical recipe at 7%, ruby milds which are kinda the modern equivalent at 6%, pale milds, Northwest milds which are rather sweeter than their counterparts just 50 miles to the south, and then classic West Midlands milds which are probably the ones you're thinking of. Ron Pattinson has researched them extensively :
http://barclayperkins.blogspot.com/search/label/Mild
In many ways the 1950s was the heyday of "modern" mild, but the absolute nadir of British brewing in general, something like this
1950 Lees Best Mild quite appeals.
Waterwise - you're away from the southeast so it's not superhard chalk water, the mains supply somewhere like Dudley is still hard-ish - maybe 200-250ppm TDS, 50ppm each SO4 and Cl - whereas Manchester water is super-soft, <10ppm for most of the major salts. So they will be Burtonising, but given the overriding need to cut corners wherever possible, I'd assume not the full Burton - maybe as low as 200ppm SO4.
Yeast - the West Midlands is particularly poorly represented among the main commercial yeast companies, you probably need to go to Brewlab if you're that concerned with authenticity. I want to try MJ M15 Empire in a mild as I suspect it would work quite well, ditto something like WLP540. But Nottingham will do.
Personallly I'm not convinced that a say 4% pale dry beer will necessarily be more calorific than a 3.4% dark beer that's full of unfermentable carbohydrates, so I wouldn't get too hung up on the mild thing. And you can go too low - for me the sweet spot in British styles is around 4.2%, you can make good beer below that but it gets increasingly hit and miss the lower you go - and bunging in a load of oats is not the answer.