Still no photos, sorry, but I did get to have another quick glimpse today.
It has the black paint finish. NO SERIAL NUMBER PREFIX to ANY of the serials, and no prefixes have been removed. The bolt is totally without a single marking on it. Floorplate is mismatched.
Typical post-war rebuild before being sent SOMEWHERE for hard service - stocked in beech, with pressed nosecap and triggerguard. Bore really is nothing spectacular.
PROBABLY a Vietnam souvenir.
Hope this helps people formulate ideas why it has no serial prefix.