unknown l'eroica replacement frame

so i love my mercian, it's served me well at 2 l'eroicas and experienced a few different setups but as it basically only gets ridden at l'eroica or on rough roads in yorkshire i've decided to trade her in for a something with a touch more tyre clearance for comfort

i got it off the forum here as a black DeVer frame with what appeared to be full chrome showing underneath in need of some loving restoration. I got it in 2012 i think and finally got round to dropping it with chris marshall to restore last summer
frame is 531 like the mercian and very similar in sizing just a touch shorter which i prefer anyway

Upon stripping, the chrome was actually not too healthy so my chromovelato idea was out. I decided on a compromise of a metallic silver main frame, exposed chrome head tube lugs, chrome dropout and chain stay, chrome seat stay caps, and chrome fork legs (painted crown). A little cheeky st christopher, the patron saint of travel medallion turned head badge finished it off nicely

just picked her up yesterday so quickly stripped the mercian ready for cleaning and passing onto another forumger (already spoken for i'm afraid)

more info to follow as i get her built up

comparison of frames next to each other

also, any help with this serial number would be appreciated - DeVer didn't make their own bikes so it could be anyone - after reading up on frame styles lug choices and serial placement a touch, maybe holdsworth or harry hall?

anyone else have any ideas on this serial number?

8 over 14 then a separate 3910 maybe?
or 8 and 143910

Holdsworth always stamped the frame no. on the steerer as well I think.