Power Query , Transform Column of Records

Hi, I have been trying to transform a column of records by another column ; I have mangaged this as an 'addcolumn' so;

Table.AddColumn(
  ToTable, 
  "Custom", 
  (x) =>
    List.Accumulate(
      Source[Name], 
      x[RecColumn], 
      (s, c) => Record.TransformFields(s, {c, (y) => Text.Contains(y, x[Item])})
    )
)

But I cannot figure how to get to the 'outside' columns when using Table.TransformColumns,

List.Accumulate( Source [Name] , ToTable, (s,c)=> 
  Table.TransformColumns( s, { "A" , (x)=>   Record.TransformFields( x , 
                                              { c,  (y)=> "Item col ? "  } ) }  ))

I have attached a workbook showing working out so far, There is an addcolumn query using the above and a query called RecordTable
which is where I've got to using transform column; so the question really is to access , in this case the 'item' column when using
Table.TransformColuimns ?

Richard.