I looked at the numbers on the Dana 60 that I have under my '65 Coronet. The BOM is 602957 3 and the date code is 12 2 8 C1.

So I think that means it was built Dec 2, 1968 and went into a '69 B body car?

I bought this rearend about 30 years ago so my memory is hazy. I think it came from a Charger but it could've been something else. I know it had front disc brakes since I bought those at the same time. I might have also bought the front anti-sway bar and the Hemi torsion bars but I'm not sure. The guy was parting the car out and I grabbed as much stuff as I could afford.

You're correct on the date.

I've always wondered, what are the different dash number (-3, -5 ....) for same gear ratio

Probably a design upgrade that might not be obvious.

Related a little, just pulled the Dana apart on my 2001 Ram Van and they have a crush sleeve instead of preload shims on the pinion now.

The previous owner of the Dana under my Savoy welded ladder bar mounts right at the end of the numbers It was drag car since about 1973 so that is how things were done back then. It was a 67 Camaro with a high winding 292 small block and a Nash 5-speed.

Gus

Same here, got my original 4:10 E-body rearend out of my buddy's race Camaro.
It had welded ladder bars and a 5:38 spool, only paid $300 for it, so I didn't mind cutting off the ladder bars and putting the original 4:10 gear set he had saved back in it.