Is this a decent deal? 8.75 rear end

$100 is a deal BUT a C body axle is WIDE (63" or so) do you have a reputable drive train shop near by you? I would call and see what the cost is to have it narrowed to 55" or so that the A body axle is..

you will need to buy new perches (the MP ones are like $12.88 on Summit)
they need to be 43" center to center

if it's $600 or so to have the housing/ axles narrowed I'd just wait out for a A body one they're are always a few on here...