Variety of answers. For mine it was regency and make sure have adequate brakes on the front that suit the weight addition - i.e. R33 front calipers etc., or 4-pot type-M R32 gtst brakes. That was from my experience. Though, you wouldn't want to keep the RB20 gearbox with an RB25DET under the hood...went through 2 gearboxes with the RB20, so chucked the 25-box in with the RB25.