SB3 bus

[LS120]

can anyone tell me what gear box & diff i can put into an sb3 300 petrol it has the 4 speed & single diff not split diff.

any help if a TK or other will fit or what would work & how hard it would be.. (to adapt)

we want to try & get better speed as it gets upto 75/80 km & would like at least 100km

any advice & help taken.

Thanks.