If possible, try to find an S54 from an SMG car. no chance it's been over-revved. You may want to swap out the intake for a 6-speed version, but they're cheap on ebay (SMG intake has a small built in oil reservoir that you won't need, and may have an inlet or two that need to be plugged). As for transmissions, go with an E36 M3 ZF 5-speed. Smaller, lighter, and way cheaper than the 6-speed from an E46 M3. And you really don't need the overdrive gear. Budget for preventative rod bearing replacement and vans seals. Try Epic Motorsports or Kassel Performance for wiring, tuning and EWS delete. Have fun!