Keeler's frame seems to have conventional lugs, but in any case it was specially built for him (he was already a star in 1957), so it doesn't really tell you much about Mercian frames.
I note this 'Mercian' sold for a little over £220, which doesn't seem extortionate for such a quirky frame.
I thought the Mercian looked similar to this one:
https://www.classiclightweights.co.uk/readers_bikes/mercian-vincitore-1957/
I was going to put Paris in speech marks but just mentioned the over the top decals instead.
Agree re the paint jobs. Both look overly restored but interesting frames potentially worth a punt.