As OZZYCB has already said, absolutely nothing sandcast about that motorcycle. Going by the numbers and if Australian delivered then this bike started life as a 1970 K0. This is an area Tom Courtney is knowledgable with
As stated by OZZYCB, this bike has a bitta this and a bitta that, so it's very hard to say what it really is now. Tank, side covers etc colors are K1 as are many other items
Sandcast it certainly isn't
One point of clarification for your info is the last sandcast "engine" produced was E7414 (not allowing for the French sandcast engines) so the seller got that wrong as he has for a number of his other statements