X2 on the drum issue. Also, I dont believe its possible to simply bolt on rear backing plates to the front but maybe you can. Hopefully someone can confirm one way or the other.
As for the ball bearings, they don't squeal, well not in my experience anyhow, when they wear out, they vibrate and grumble. No, you cant mix and match bearings so you cant install a tapered outer bearing in a stock hub (they made tapered bearings for the stock hub at one time but I have not seen them for probably 30 years or better.) The key to the ball bearings is to keep them clean and packed with fresh grease, and to install and adjust them according to the shop manual, with a torque wrench, to set the bearing into the race and to put the proper preload on the cages and balls. Mine are 30 years old, at least.
When they do go bad, you might consider changing over to the tapered bearings. The tapered Bearings are cheaper and can take a side load better.
Changed out the backing plate with a fair used one that had very little wear on the plates. I drove it around the block (about 3 miles) and so far I'm hearing nothing. Hopefully it's fixed. I've had (11) 57 Chevys and all kinds of other cars, put brakes / pads on many of them but never changed a backing plate.