Definitely Raleigh
A few photos from my (known) '57 Lenton Grand Prix (first year actually before catalog introduction)
5 numbers, 2 letters
this Raleigh s/n system began in 1955 - in '61 moved the RA/RB WA/WB up front and added a suffix letter (per Kurt Kaminer)
Most likely, the letters are in series,
which would make your bike later than mine, but certainly '57-'61
There's no additional s/n logic for these bikes on the net, other than finding dated examples and comparing serial numbers
@LouB - what's the serial number on your '60 Lenton?
I'll try to get this from Lou and see how it compares.
@SirMike1983 may have some great data points for this
Where should you begin? Build stand is helpful, but variations on it work, such as straps hanging from solid ceiling hooks. Wheels and chain off, clean the chain; all the bearings (headset, bottom bracket, front hub) have to come apart for cleaning (maybe loose ball replacement) and lube. While it's down, good time to rub the paint with Meguiars. If you look under the Restoration page, you'll find remedies for the rust. 301 Protectant is great stuff for cleaning old plastic.
May need new cables, not necessarily cable housings. Great idea to spray Boeshield through those old cable housings (pucker and blow it through, repeat until it comes through clean). Almost certainly will need new tires and tubes, but those are easy to find.
As far as lube of the SW hub, it's not something I've ever tackled, so might want to hunt around or ask some of the SW experts here what's involved. Might also want to check Lightweights page on this forum for more specifics.
You can find YouTube for just about anything, and Park Tools is a great reference
https://www.parktool.com/blog/repair-help
The late Sheldon is also a great resource
http://www.sheldonbrown.com/glossary.html