I'm thinking more Prisma/Delta - and I don't mean Delta Integrale, more Delta non-Turbo 1.5...
What makes us so sure they're not off a Y10? Of course, I've hardly ever seen a Y10 myself
From an engineering viewpoint, that slot for the valve looks like a major structural compromise, but then again I never did all that well in 'strengths of materials 208B'. It just looks like a stress-raiser to me!