need 8 1/4 advice

At 300-ish HP, your worry level should be zero.
At 400-ish HP, your worry level should still be zero.
When you start getting to 475+ HP, upgrade your axles and use a quality Sure Grip for no worries.
I can not attest to the quality of the diff's your looking into. I have not had an issue with the factory parts.

From what I understand, using a Dakota R&P is not a issue.

For zero - 60 mph runs on the HP level of your engine, you have nothing to fear. You could gear it higher.