From what I've seen and casually tested:

Parry seems to be 20% damage mitigated, ALWAYS, regardless of strength, weapon or level.

Block does vary but seems to be a function of your shield's Block Value vs your Level. Strength does not affect it. My Aegis Zeta was blocking 25% damage at level 51 and as soon as I dinged 52 it started blocking 24%.

So I think we can probably assume that the only thing that affects your Blocking is the rate/value on your shield relative to your level, and the only thing that affects parry is your Parry stat which only affects the Rate. This basically slightly diminishes the power of a Strength tanking build relative to pure Vit (though not enough to stop you going full Strength when you're geared). It also probably means that Tower Shields will become by far the best shield option now that Sheltron is in the game.

As for whether Dex still affects the change to block + parry, I'd -doubt- it but we we wont know with testing.