I found an app that will check that your Mac can boot 64 bit and reset it so that it boots 64 bit without having to hold down 6 and 4 as per the Guide.
Startup Mode Selector:
http://www.ahatfullofsky.comuv.com/English/Programs/SMS/SMS.html
Startup Mode Selector:
http://www.ahatfullofsky.comuv.com/English/Programs/SMS/SMS.html