Rear suspension... HeLp

I have a 69 dart with a factory 8 3/4 and 9 inch slicks. I plan on building a much larger motor for he car. I am currently running s/s spring and a piñon snubber. My question is how much power can a 9 inch slick take and what is the best rear suspension to help plant the power. Guess that's two questions..:( and feedback will be appreciated.