Not a problem. The 1975 dizzy has vacuum advance. If it pings under load, set to 10, then you might need to either disconnect/plug the advance, or retard it just enough so it doesn't ping, but still seems more lively than stock.
With respect to the difference between the 1975 and the 1984, yeah, the '75 is going to be much more like a 145E. It still has the 240 suspension and floor pans, but it'll have the 140 feel, along with the 140 sounds...
Yeah, I thought about modifying a 245 wiper stalk to act as a secondary OD switch in my 242. Hit the button on the end of the stalk, or hit the button in the knob, depending on which is easier. That said, I may be downdating the car a bit so I have both my 242 and my 245 matching, overdrive setup-wise. Installed the 1975-80 setup on the 245Ti.
-J