Will a Stock 489 handle 700hp?

If you are not launching it hard you might be fine with the 8 3/4....just know that sticky tires and a hard launch could break it.

Might as well mention this too, my 8 3/4 has held up fine over the years. It has survived years of nitrous launches (~9 years) and the more recent (the last 11 years) is has survived stroker motors beating on it almost every weekend in the 10's. This is on a 3250# footbrake car. I know that I'm on borrowed time, but just know they can survive.