The stock points coils are 3.9 ohms. Most aftermarket points coils run from about 4 to 5 ohms. The TCI coil is 2.5 ohms.
After market ignitions use several coils. Early Boyers use a high ohm coil like 4.5 ohms. The later use a .6 ohm coil.
The Pamco uses a 2.5 to 4.5 ohm coil.
CDI coils can be very low ohms, like .1 or .2 ohms
So does the 400 use points? if so then they will work on your XS650.
Leo