Hi Mike,
you're welcome, all very interesting for me. I can only assume, I think reasonably, that they became Mormons simply because that was clearly an important religion within their relatively small local community, perhaps their friends or relatives were already Mormons ?. As suggested I'm sure contacting the Gadfield Chapel/museum will shed further light on this. Perhaps they even kept records of names etc ?.
And as to numbers, I'd assumed you might be already knowledgable on the Mormons, if not one yourself, I don't even know where you are now ?.
As a Cinderford Forester myself this whole Mormon situation is completely new to me and I must say quite surprising. Then again until I discovered this great forum last year I'd never imagined there was such a variety of religions & chapels etc in the Forest, coming from a CoE family I'd rather assumed that was the norm everywhere. Until yesterday in my thinking the Pendock/Staunton area was "just" a fairly sparsely populated rural farming community.
As to the numbers who went to the USA, as per the website link above:

"During the mid 1800’s the western USA was settled by thousands of British emigrants from Herefordshire, Worcestershire and Gloucestershire.

Their story, and their journey, began here....

In 1840, Apostles of The Church of Jesus Christ of Latter-day Saints (“Mormons” or LDS) travelled from their headquarters in Nauvoo, Illinois, to the three counties and taught the local people the fullness of the gospel of Jesus Christ. During the next 9 months, 1,800 people were “converted”, including almost the entire membership of a local Christian organisation, known as the United Brethren.

In less than two years most of the converts had left their homes and sailed across the Atlantic..."

Re the Gadfield Chapel itself, just a few mile from Brands Green, to reiterate:

"The Gadfield Elm Chapel near the village of Pendock in Worcestershire, England, is the oldest extant chapel of The Church of Jesus Christ of Latter-day Saints (LDS Church).

The structure was built in 1836 as a religious meetinghouse by the United Brethren, a group of breakaway Primitive Methodists led by Thomas Knighton. In 1840, Latter Day Saint missionary and apostle Wilford Woodruff preached among the United Brethren; ultimately all but one of the 600 members of the United Brethren were converted to Mormonism. After the conversions, the structure was deeded to the Church of Jesus Christ of Latter Day Saints by Knighton and John Benbow.

As a chapel of the early Latter Day Saint movement, the building was a centre of activity for the church in the Malvern Hills area. Several regional conferences of the church were held in the chapel, and Brigham Young, who at the time was President of the Quorum of the Twelve Apostles, spoke there at least once. The chapel was sold by the church in 1842 to help fund the emigration of British Latter Day Saints to America."

Jeff.