First of all congratulations on getting such a nice bike! Eddy the owner and painter before his accident, painted the first couple of bikes I made after coming back from England where I learned in 1975. The Hellenic seat stays were kind of their signature look. When Eddy was no longer able to paint, someone that had a frame made at Cyclery North had me paint their frame. I took it for a test ride and discovered that Hellenic stays rode differently in a way I liked. I bet you'll like them too. One of my custom frames I made for myself has Hellenic stays.
There are several cautions I would give about changing the bicycle to fit your more modern taste starting with using Velo Orange Porteur bars. Those kind of handlebars need a slacker seat angle than what is common so you body is positioned properly while riding. In addition a longer top tube is required (which yours certainly is) because your hands are coming back from the stem not going forward. Looking at your pictures it does look your bike has a swallow seat angle. For reference i find that with sweptback bars, a seat angle of 73º is intolerable and 72º is uncomfortable for me. Bike frames for upright bars need to be 71 degrees or less.
A Henry Jame fork crown has about 42mm of width between blades. You can get a 32 or a bit wider tire comfortably to work with that crown. We almost never built bikes with fenders in that era. They just were not cool. It makes no sense to butcher the history of this bike to try and use wider 650B wheels.