8 3/4 in a 69 Valiant

I recently became the proud owner Of a stock 69 Plymouth Valiant, 255 /6. While driving it around the for last two weeks I've noticed a rumbly-grindy sound coming from the rear end (pretty sure it's a 7 1/4), after some research I now think I have a bad wheel bearing. I've look into doing the job myself and believe I am capable if I can find a place to press on the new bearing. Then today I found a 8 3/4 Rear on a 72 or 73 dodge truck (casting # 2881489), I can get drum to drum for for $160.00. So what I want to know is should I fix What I have or pick up the 8 3/4 and what difficulty's would I face doing this.