I have spent some time looking at N54 options, fantastic, willing, strong motor, 10+ year old vechicle, 100kms, worth 10-15k$ tops, so price has to be factured.
I have punted with the Mamba brand, ( Ex Kinugawa CEO Japan) product is mainly larger single BB race, drift, rally units, with US, AUS, ENG outlets.
Was around NZ$1700 delivered, for sort of stage 1.5 new, upgraded hybrid new CHRA's with new 14T comp housings and wastegate upgrade kit.
Had some correspondence with owner, says only best, new cores, metals, bronze, stainless used are sourced from US or Japan.
They have big range Andrew, have a look for your ride, may find slight upgrade at fair price.