I would consider swapping you two G12T-75's for two V 30's, but I would also keep the V 30's if I were you. I'm SERIOUSLY considering getting one of those cabs, and man did you get a good deal on it! Here's some info on the speakers:
Celestion Vintage 30
Series: Classic
Power Rating: 60W
Nominal impedance: 8Ω and 16Ω
Sensitivity: 100dB
Voice coil diameter: 1.75", 44.5mm
Voice coil material: Round copper
Magnet type: Ceramic
Magnet weight: 50oz, 1.42kg
Frequency range: 70-5000Hz
Resonance frequency, Fs: 75Hz
DC resistance, Re: 7.3Ω & 12.9Ω
MSRP: $215.00
Celestion G12T-75
Series: Classic
Power Rating: 75W
Nominal impedance: 8Ω and 16Ω
Sensitivity: 97dB
Voice coil diameter: 1.75", 44.5mm
Voice coil material: Round copper
Magnet type: Ceramic
Magnet weight 35oz,: 0.99kg
Frequency range: 80-5000Hz
Resonance frequency, Fs: 85Hz
DC resistance, Re: 6.77Ω & 12.9Ω
MSRP: $160
And the Cabinet:
R412CB
Straight, angled baffle
Power Rating: 280W
Speakers: Vint 30's
Inputs: 4Ω/16Ω mono, 8Ω stereo
Made U.S.
MSRP: $1,099.90
I'm quite certain it comes with the 16Ω speakers.