Were OEM bearings the sealed type?

if you have an 8 3/4 axle, then no, the right axle should have an adjuster on it. The stock axle bearings look like



instead of the green bearings that look like this:

OEM bearings were of the tapered roller bearing design. There is a inner grease seal pressed into the axle housing and a seal in the axle retainer outside of the bearing. It is the inner that will start to leak rear axle lubricant into the bearing area and then into the brakes. You don't want this. The only lubrication the rear bearings get is from the wheel bearing grease that is packed into them during installation.

I just took my axles up to NAPA to have them replace my bearings.....the machinist looks at my existing bearings and says "You know, usually, the taper is the other way"....basically saying the existing bearings are on backwards?

I have never replaced these since I've owned the car and I've not had any issues up until my seals giving way and having the grease washed out on them this past summer.

Does this make any sense? I told him to put the new ones on the same as the existing ones at this point.

Any ideas on what he's seeing? Is it even possible that the bearings could be on incorrectly and yet I have had no problems installing them before or setting the end play, etc?

He has me worried.

Also, are there any seals under those bearings that would need to be replaced once he pulls the old retainer and bearing off?

Thanks

Look at the above picture. This is the correct way that they should be on.
Still wonder why you wan them replaced. If tehy are good all that they should need is cleaning and repacking with wheel bearing grease. replace the inner seal so that rear end lube. doesn't get into them and go for many thousands of miles. IMP save your money for shes for the kids or something else needed.

I was hearing a groan when turning last summer.

In the picture above from the archives, it appears to me that this is how mine are set up...with the larger diameter of the bearing to the INSIDE....the Napa tech was saying that "usually" the larger diameter would go to the OUTSIDE....

So there is a seal under that bearing between the race and the mounting flange, correct?

The main seal to worry about is in the housing.
The seal that is in the retainer is only replaced when the bearings are replaced. So in your case replace it. But be sure to replace the inner seal that is in the axle housing. This is the one that keeps the rear end lube out of the bearing and brake area. Make sure to pack the bearings with a good wheel bearing lube. this is the only lubrication that they get. Check this out for reinstallation: http://www.moparts.org/Tech/Archive/axle/12.html