Dave,
Mk3 diner had only one toilet on kitchen side pic 2,the other side had lockers for staff then they were removed in early 90s to put card phone in, there was never a window on this side of coach.
The door's at kitchen end are normal not plug for loading, the door's look over scale like off a mk4? your better sticking with a Hornby/Lima mk3 and get casts done of silver frames as the coaches are std english mk3 no different.
You have roof vents in middle of roof, irish had three above second white kitchen window for deep fat and grill.
Hornby do a 4 window diner R4339? not far off irishrail bar one window in kitchen which could be painted on,i picked up 4 from hattons for @60 quid last year just now need to paint and change toilet window as well on one side also hurst still do the Mir one in brass that was around a while back.
Rain water strip over doors, looks flat on model.