Thanks for the interesting information and history
@Paul_Smith SRCC . You’ll be pleased to know that, thirty-ish years on from when you built it, the bike never fails to put a smile on my face.
You're welcome, looks very original, 3ttt stem and bars (from
Chicken Cycles at the time), Silca pump and Rolls saddle (from
JD Whisker) were all items I would have used in the build back then. I'd had hand built those wheels with Ambrosio rims (
from RSI) I think I can still see the red 'handbuilt by Pearson Cycles' sticker on the rim?
If I was to try and date the bike I'd say about thirty years, we definitely didn't do them when I first started; we used
Tudor Sports, famous at the time for clothing and as you can see they still exist, although with a different owner; back then they also supplied frames. We didn't sell the
Simocini built frames towards the end of my time there either, we had been using them as a budget yet good quality frame to compliment the higher spec' UK built frames that we sold at the same time; built for us by
M.Steel/Dave Yates. The UK built frames were normally Reynolds 531C for the race frames and 531ST for the Audax fast tourers and were initially more of an investment as they were full Reynolds tube sets, forks included, as opposed to the three main tubes only being Columbus on the
Simocini. Over time the prices increased driven by the exchange rate effectively made the Italian built frames the same price as the higher spec" UK frames which made the less far less appealing of course; as a result we stopped supplying them.
I still have two thirty year old Pearson 531 bikes, I'm cycling on one later today!
Regarding the cable routing if you lubricate the cable channels on the BB shell and clean that section on a regular basis you should find it ok; being so exposed they can get clogged up quite easily. It was pretty much standard to have a bike set up like that back then, it just needs a bit more regular tlc compared to a fully enclosed internal cable. I actually still like bikes like that, far easier to work on and simple and I for one enjoy cleaning and fettling my two wheeled friends, all my bikes even my more recent purchases, like my
Van Nicholas Chinook and
Yukon below have full external cables; mind you I say recent I bought them thirteen years ago !
If you are replacing both cables you could also clean up that rusty area carefully with wire wool then use something like
hammerite to protect it. The bottom bracket shell is quite thick, eventually steel frames can rust through, normally it will not be the BB shell that gives up though, but none the less I'd still clean that rusty section and treat it; just because I could!
. 
