It says RD, but I think it's more likely to be an RZ if it has YPVS. But this is greatness!! I could see @Tabasco doing something like this.
Mad Genius Sticks A Yamaha RD350 Engine Inside A 1960s Lambretta Scooter (msn.com)
Mad Genius Sticks A Yamaha RD350 Engine Inside A 1960s Lambretta Scooter (msn.com)