I have a 360 that's around the 400 hp mark. I have a handful of passes at the strip on the car and a lot of street miles on the car with the slicks. I have a 8 1/4 with 3:55s and it is holding up great. I'm not sure at what rpm I launch but I had 1.9 60 ft times. On the street I am very rough on it too. It's not a four speed car so it's not as bad but it will give you an idea. That being said, if I was in your position I would save up for a Dana just to be safe and because you will want more power and you wolnt have to worry about your rear!
Btw stick with the four speed. It's much more cool to watch and a lot more exciting to race I am sure.
