Hi SIS,
No problem - here are the dimensions:
Power PCB 126mm x 96mm (this is close enough to 5" x 3.78")
Amp. PCB 125mm x 77mm (each channel) (5" x 3")
Supplied heatsink 300L x 45D x 75H (11.8" x 1.77" x 2.95")
Yes, you can split the power supply pcb into two halves, one for each channel. The dimensions then are 126mm x 47.5mm for each half with a 1mm cut width.
You can also cut the aluminium heatsinks in half, but they are 8mm thick at the base, and this requires quite a bit of effort, particularly the finishing after the cut. You might be better advised to use a 100mm tall heatsink rather than the 75mm supplied; this will cost a little more, but should mean you can build a case with a heatsink on each side but adequate cooling for three channel. I must stress that you can't be too careful cooling an amplifier; ambient temperatures are high at Mt Newman and too much heat at high power, specifically into low impedance speakers, will kill an amplifier fairly quickly.
Hope this is helpful.
Cheers,
Hugh