I was searching for a thread that verified this but I could find one.
A G73SW can take the GTX560m card from a G74. It "bolts" on directly. There was no need for a VBIOS/BIOS update and I didn't even have to uninstall my graphics drivers. I put it in and powered it on with no problems.
On a side note;
The thermal paste, or whatever ASUS uses, is really gunky and thick. I replaced the thermal paste on my GTX 460m with Arctic Silver and got my card to stay ~6-10 degrees cooler while gaming.
CombatDork
"Common sense is not so common." - Voltaire