Google "Nardo Supra" and you'll see the monster that one Mr "Smokey" Nagata of Top Secret made, he made it blown and very fast. Namely the Supra is named for the Nardo Ring proving ground in Italy, the target was 400km/h and it's rumored the engine pushes out well over 1000bhp and some insane torque figure like 800ft/lb which is kinda 'nuff said lol. In all fairness if the same development was done as the 2JZ-GTE engine which as an 3.0 inline 6 can produce over 1000bhp with the right tuning I'm sure the 2000bhp mark would be more than achievable, would drink like an alcoholic on a hot day and need all the performance bits you can buy thrown into it and all tuned and balanced to within an inch of it's life but there is room to up the displacement and the crank is billet as stock so more than tough enough, forged rods and pistons with race bearings, full top end build (48 valves though

) port and polish, decat, free flowing exhaust and manifolds etc etc. Pretty sure a lot of off the shelf 1JZ and 2JZ parts would fit with regards to internals, maybe find someone to make some custom cams for a more race oriented engine.
As always the one big question, how deep are your pockets?
The Top Secret Supra runs twin ECU's each controlling one half of the engine, not sure if they ditched the MAF's for MAP's but there are 4 knock sensors to hook in too and the plugs are twinned up physically too on the stock system, each plug has a coilpack the a little fly lead to it's paired plug/coilpack. The options for replacing the CAS with aftermarket ones like the AEM ones could also open up a lot of possibilities. Completely stock an in a Century the engine is designed so it can run off of just one bank on cylinders if needs must which adds a lot of complication, starting with a bare engine and wiring loom would be a better option but again it's drive by wire so throttle control ECU or mods to hook up twin butterflys to a cable accelerator.