The Soundex function on FreeREG dos not realise Michell is a variation of Mitchell, so you need to search for both spellings.
There is a marriage in 1658 at Doulting of Mr John Michell of *moone and Mrs. Mary Spearing of Chuton. The first part of the groom's abode is quite illegible and I have no idea where it could be. Doulting is about 13 miles from South Cadbury, but it's also about 10 miles from Chewton Mendip so that doesn't completely rule out this wedding as a possibility.
I can't see any other candidates. Note that the 1650s were the Interregnum: at times marriages were performed by magistrates not in church and even if they were recorded some records were discarded at the Restoration.
Moving on to the 1680s, there is another baptism for John and Ann: Joane in 1691 (FreeREG has 1689 but although the entry is in a column headed 1689 it is dated 20 May 1691.)
There's also a burial at South Cadbury of Sarah, daughter of John Michell of Witcombe and Mary. That's interesting as it probably refers to one of the villages which are nowadays called North and South Widcombe, which are in the Chew Valley and not far from Chewton Mendip. That makes the Doulting wedding look a better fit. (There's also a Widcombe near Bath, but that's even further from South Cadbury. Either way it shows the Michells moved around.)
David
Oops, there's also a Witcombe in Corton Denham, just south of South Cadbury and the SHC has leases of land in Witcombe to Michells of South Cadbury in the 18th century, so the Doulting wedding goes down again in likelihood.