Righto, thanks guys, I just had a quick look at jaycar site, I'll most likely use these speakers:
Precision Response Kevlar Coaxials - 6.5" 2 Way
Power Handling: 75WRMS
Impedance: 4 ohm
Voice Coil Resistance: 3.9ohm
Vas: 12.183
Qms: 3.401
Qes: 0.666
Qts: 0.557
Sensitivity: 91.3dB/Wm
BL: 4.981 TM
Dimensions: 157(Dia) x 77(D)mm
A: 157 B: 148 C: 78
I don't think 77mm will be too deep, but I'll check it beforehand anyways.