Nifty Bullpup AK

This image of a DIY AK bullpup conversion has been making the rounds online for years but I had not seen it until a reader email it to me. I cannot identify the 7.62mm AK (or derivative) it was built on. Does anyone know? Some have suggested the VEPR Hunter, but the hinged receiver cover, rear sight and funky gas block do not match.
video
video
UPDATE: It is a 7.62×51mm NATO Valmet Rifle. I should have known that!