"Does it go in as one unit "pressed" in with the retainer plate or should I separate the bearing race and install it first to make sure it seats properly?"
This may be a little late, but this is a quote, word for word, from my shop manual.
1.Install the outer retainer plate (if it had been removed) making sure it is not put on backwards.
2. Place the new lubricated seal and lubricated bearing on the axle shaft making sure the cup rib ring is facing the axle ******. It should be noted that the seal used on a drum brake vehicle is different than that used on read disc brake equipped cars. The seals are not interchangeable. To identify the seals, examine the outer rim. Those used with drum brakes have a gray metal appearance. Those used for disc rear brakes have an orange-colored appearance.
3. Press the tapered-bearing and seal assembly on to the axle shaft. Apply sufficient pressure to seat the bearing against axle shaft shoulder. Do not attempt to press the bearing retainer at the same time.
4. Position the
NEW bearing retainer on the shaft, then press it into position firmly against the bearing.
5. Apply Multi-Purpose Long-Life Lubricant C1AZ-19590-E (ESA-M1C75- B) or equivalent to the outer diameter of the cup and the seal. Install the brake backing plate and attaching bolts.
6. Before sliding the shaft assembly into the axle housing, ensure that the outer seal is fully mounted on the bearing.
7. Carefully slide the axle shaft into the housing. Start the axle splines into the side gear and push the axle shaft in until the bearing bottoms at the housing.
8. Install the bearing retainer plate plate and the nuts that secure it. Tighten the nuts to 28-54 N.m (20-40 ft. lb.).
9. Install the brake drum.
There are a couple of pictures if you need them. Hope that helps, never did it myself.
Good luck,

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