...here is a photo of an early Raleigh Super Course. It seems to me to have about all the inherited characteristics of the Lenton Grand Prix, albeit with an upgraded fork and a slightly less ornate paint and decal presentation. They used to be pretty commonly available, and more numerous because of their early 70's origin, as opposed to 1950's. What's nice about this choice is you can still find them with the original cottered cranks, if you want that as a feature.
If you really wanted to go hog wild, you can get decals that approximate the Lenton ones from H Lloyd in the UK.
https://h-lloyd-cycles.myshopify.com...raleigh+Lenton
You'd need to mask the lugs and head badge, and paint the head tube to get that look. But that's not difficult to do.