Hi Jim, I can't help you with your research, I don't think but as one Marshall to another - I think they are a dime a dozen in England - I have traced my ancestor Thomas Marshall b. 1796 to Glouchestershire. He married a Sarah Hobbs and lived in Chipping Sodbury. I did get to met some relatives the last time I was in England.
This may sound off the wall but this is how I found them, I went to the British phone book in the area and found all the Marshall's I could, I sent a letter to about 20 of them, just saying I was doing family research and lo and behold I got two replies. I was needless to say shocked, but I have kept in contact with my new found relatives. They don't know much of the family history and as a matter of fact I took over a large folder of the family info I found and gave it to them. I do have Marshall relatives in the US but have never been able to locate them. The last I found on the census was Robert Marshall living in Mass, I think and George Marshall in Colorado. I hope you have good luck tracing your family.