TR6s here, too- almost 15k miles on them, they look great... Tuned up to 342fwhp, just got my SVT cams to replace the 3L/Mazda 6 combo that ran out of steam around 4500RPMs...

400fwhp should be reachable with the SVTs in there... I know the turbo's up to it, and I know the engine will hold.

Dan G. and his Cougar Forged internal (Diamond & Pauter) full 3L, "Monster" Kinger F/I cut & P&P, T3/4 60 trim .82A/R ADC turbo, SPEC Stage 3, Torsen, Greddy Profec-B SPEC II, Apex'i Timer, Lots of Gauges! Used to have: 3.0L SVT hybrid