The safety position is the most obvious feature. Crossbolt on the 88 and Tang on the 500.
Other than that I think most parts are interchangeable.
Ok, I'll say it...
870
there both a 5+1What will be the main purpose of this shotgun? If for home defense and on a budget go with an 88 one can be had for around 200 bucks then mount a quality light on it and call it a day.
If your planning on doing some more modding to it then go with a 500. The forends cannot be swapped out on an 88. The safety locations are mounted in different locations between the 2.
Which models are you looking at the 5+1 models or 7+1? You cannot add a mag extension to either or thats why I ask