Does the 74 - 78 all use the same ignition setup?  flywheel, points, condenser, coils, plate. etc?   I may have found a 75 bike, at least I think that is what it is. 

Not sure exactly what you are asking.  Generically, they are "magneto points ignition systems".  

Specifically, they are NOT identical from year to year during that period, but you can make a "matched set" from a 77 work on a 75 for example by swapping all the components and adding a regulator.  

(Alan probably knows for sure but I seem to remember 74-76 ignition was Hitachi and 77-78 was Mitsubishi)

Part numbers suggest that all models use Mitsubishi parts (ie the part numbers end -2...).

I would bow to Mark's far greater knowledge and experience on whether or not complete setups can be interchanged - I don't know the clearances needed for the inside of the points cover, how long the end of the crankshaft is, or the wiring/terminals arrangement.

74-79 250/360/400had a smaller opening in the case and a slightly smaller flywheel than the 68-73 250/360.

Physically, the 74-79 systems fit 68-79 for the 250/360/400.

The 68-73 250/360 will usually not fit the 74-79 because of the slightly bigger flywheel OD.  

Output power and wiring changed slightly as the bikes got newer but wiring can be adapted fairly easily to work if you swap complete systems (ie you need to swap the stator and flywheel as a matched set.)