Matchless ?? '63/'64 Buick Riviera. The bike. Mid-59 plate. The bike. Royal Enfield but a single or a twin (with siamesed exhaust) buick riviera 63 Buick Riviera. This page is for the bike, not the car!
Thumbnail #1 evidences single cylinder and looks too small to be a RE twin, so quite likely a 350 Bullet Airflow. Adjustable(?) rear dampers seem set an angle which would embarrass a Velocette. Its rider has all the gear, anyway.