Tuscan engine upgrades?

[TUS 373]

I have noticed on some of the Tuscans for sale in the classifieds that they have had engine performance uprated to RR/S spec. Now, I may be getting hold of the wrong end of the stick - but if I am getting this right, they are tuning/modifying the 360 bhp 4 litre upto 380/390 bhp. Can anyone confirm that they have had this upgrade done and what the practicalities of it are?
Thanks
Bryan

[TUS 373]

Where I am coming from is - if you a standard 360 bhp 4 litre engine, has anyone had this converted into RR/S spec retrospectively and uprated the performance to 380/390 bhp?