73 Firebird which motor?

[1973Firebird01]

I have 73 Firebird that I'm very close to doing the motor in. It currently has a Pontiac 455 (.30 over) with a TCI TH400. The car has a 6 point cage, (install next week) BMR Gen II Torque Arm suspension, DSE minitubs & SFCs, 9in w/3.50 gears. The front suspension has not been decided on yet. The car will be driven alot in nice weather, auto-x, and see track days. I have a 6 speed for it and EFI is a must!! I have a 6.0ltr LS with LS3 heads and a 496 (minus a few parts). Which motor would be all around best.....reliability is a MUST!! Thanks in advance!!Attachment 43943