Time Machine questions

Situation

• Time Machine A : FireWire drive, used on iMac A up until January 2012
• Time Machine B : USB drive, used on iMac B up until present (not all data from iMac A is on iMac B)

Questions

How do you connect a non-current Time Machine to a Mac? These are my assumptions :

1. In SysPrefs, turn TM OFF
2. Connect TM drive to Mac
3. Enter Time Machine and browse for data to restore

Is this correct? And will it work EITHER for connecting a newer TM to an older Mac to bring it up to date, OR an older TM to a newer Mac to restore missing older data?

Or, would it be a lot simpler to just connect one Mac to another using Target Disk Mode, and restore data that way? (To me, it seems that Time Machine would be the logical way to go, as I would only need to use one Mac at a time, and just connect a Time Machine to it that isn't / wasn't the last one used).