Excellent idea by the way EGD. Not sure about it being tied to a day of the week. As you've mentioned Cotswold-Severn long barrows why not start there. I had a Cotswold-Severn Long Barrow summer three years ago ... and fell in love with the place in the process. Last weekend, still feeling quite tired from my trip to Lewis ... went for what turned out to be a restorative walk through the buttercup meadows and wild garlic woods of a very small corner of the Cotswolds. Nowhere seemed fairer.
Was given a book a while back called "Prehistoric Gloucestershire - Forests and Vales and High Blue Hills" by Timothy Darvill. Put on bookshelf and quickly forgotten about. Now have taken it down and it is open at 'Hunter-Gardeners (4000-3000BC)' - will come back when finished reading the chapter.