probably a dr diff question. or andyf.

I don't know b-bodies that well.
I know for c-bodies, which doesn't exactly help, that in 69 the spindles changed.
everything bolts up from 65-73, suspension wise. whole setups will work.
but you can't swap individual parts between them.
Like the rotors don't work between certain years. 68 won't work on a 71 etc..

I imagine part of it is the budd disc system that went away in 68.

The other question would be are you sure it is a factory disc system and not an aftermarket?

Are you sure the previous setup was aftermarket? For a long time it's been a popular mod to swap mid '70s "A" body disk brakes onto '62-'65 "B" bodies. Conversion included "A" body spindles. I don't know if the bearing diameters were different but you might measure the difference between what you took off and what you're trying to install. If its not going on far enough to engage the nut then the bearings aren't seating and you'll destroy the rotors and or the spindles pretty quickly.

the inner bearing wont go on deep enough to fit the locking nut with the washer and not enough thread engagement to put the cotter pin in.

The inner bearing should go all the way up to the raised shoulder on the spindle; if it won't, the bearing inner race diameter is too small. Do not attempt to run the rotor if the inner bearing isn't up against the shoulder.

66-69 B disc spindles
70-72 B/E disc spindles
73 up spindles

66-69 B Bendix calipers
70-72 B and 70-74 E KH calipers

66-69 B rotor Bendix

70-72 B/E rotors KH small bearing

73 up Rotor KH large, plus dia changes

Many combinations so you really need to determine what spindles you have. If 66-69 spindles that is your problem matching up either caliper or rotor. Both must be Bendix

OP stated that the brackets "bolted up fine" so the spindle must be drum brake and the '62-'69 B-body drum brake spindles are all the same, even same part number.

Yes but, as you stated earlier, the Strange kit is for drum spindles so would their brackets fit any disc spindle?

If you purchased the Strange kit for a 1969 "B" body and you're replacing disks that are already on the car then the problem is the spindles. According to Strange that kit "Fits factory drum brake spindles."

I suggest you try to find some stock '69 "B" body drum brake spindles. They shouldn't be that hard to find and if you indeed have that kit, everything should fit properly. That said, putting the later spindles on a '65 may change the geometry slightly and effect alignment. I'm sure someone will chime in who has done that before. If not, ask your question on the "For B Bodies Only (62-65 forum). Lots of early "B" body knowledge there.