If it was me building it I wouldn't be putting a V8 in it (Even though I'm a big fan of the LS series). I'd use the Aussie 4litre straight 6 turbo engine.
The Sagaris had a N/A 4.0 24 valve straight 6 in it so this is in keeping with that. The Aussie turbo 6 is a monster. Tuners down here are making huge HP with them.
Even in factory trim they are beefy. The FPV F6 Typhoon makes 416 ft/lb of torque from 1950 to 5200RPM and 416 HP @ 5500RPM.
Check it out:
http://www.fpv.com.au/fpv-range/f6/overview.aspx
Cheers