I'm pursuing an alternative boot drive so i can explore a yosemite or elcapitan environment from my old mac pro 2,1 currently in the last version of snow leopard. (with legally purchased soft ware from our new laptop) I have the pikers boot.efi files swapped out in my yosemite clone disk and am going to put it into the mac Pro 2,1. I know the video card may have an issue showing verbose boot language but it's a 512 MB nvdia so before i purchase a new one i'm going to try that first.
If I want to be able to have two different OS versions (and keep old software tools functional) running on two different boot drives in the same machine and be able to choose which system with each boot using the option key held down- will that be possible with the existing firmware (it is 64bit capable) or will i be flummoxed by firmware or other factors?
Any advice on hazards to the machine and reverting again if experiment fizzles appreciated. This would be a very clunky cheese grater.