Dyna 3.0 ohm(green) coils work well with my '79cb650.
I mounted them in the stock locations for the coils, but there is LITTLE spare room for the wires coming out of them, they do rub the tank.
On a '80 and later cb650, there may not be enough room to get them to fit without a mounting plate made for them.
I would say they are a good upgrade, especially if yours are cracked.
l8r