Starting to get things planned now Hank !
You have the choice of flying into Edinburgh in Scotland. Manchester in the North of England. Or Gatwick / Heathrow which both serve the London area in the South of England. You can get a Train to Paris to end your tour with a few days of Culture in a foreign language ! Fly back to the US from Paris will save you hundreds of Dollars because you wont pay the UK "Departure Tax" but not vital !
Liverpool is less than an hour on the Train from Manchester.
Chester is less than an hour from Liverpool on the Train.
Conway Castle is less than an hour from Chester on the Train.
All are local Commuter Trains and no pre-booking. 30 minute service all day. £2 each.
Chester is filled with Roman and Tudor Architecture. Art and Historic Buildings. Great for a day with plenty of Pub Food ! Street entertainers and Boat Rides on the River Dee.
Even my local Church here in Liverpool has been doing Sunday Services since 1100 AD. So you'll see examples of Architecture everywhere. Liverpool Cathedral was the biggest in the World, Then St Johns in NY went slightly bigger. You can even do Dublin - Ireland for a day with Ryanair. Out early and back late on at 9 pm. Good prices when booked in advance - maybe £20 each way ! May and June gives you long sunlit days. Light from 4am until around 10pm.