Yes, the only Mk.3 belt/lift this needs is the input line, which you build into the splitter! It immediately splits into 3 different belts (270/3=90) so only Mk.2 belts are needed until the next splitters which are another 3 way split (90/3=30) where only Mk.1s are needed. There's a final 2-way split into the gens themselves (30/2=15) so Mk.1s are used there. You could upgrade everything, but since this is fully load-balanced and gens only use 15/min, nothing would run faster than it does already and you'd just waste some steel. If you designed this as a manifold, then yes, you would need Mk.3 belts and you'd also have to wait a lot longer for the buffers to fill and for the last gen to turn on. So long story short: this comes online faster than a manifold design and uses cheaper/easier components to build.

why are you using mk1 belts & mk1 Lifts please??? I am feeding in coal with mk3 belt