I need some help from ya'll. Building a cab and I have a question about Ohms.

I've always had it in my head to build my own custom cab. And I recently picked up a Carvin RL410T from my drummer for my Ampeg PF500. I decided to take the speakers from that and put into my own cab.

What I'm currently working on are two 210s that stack and latch together. And that's where my question about the ohms comes from. My head runs at 4 ohms the Carvin cab is 8. And at 8 ohms my head only puts out 300w. I know two 8 ohms cabs will equal 4 ohms and the max 500w from the head.

Will my two, 210s with 8 ohm speakers equal the 4 ohms needed for the max power from my head?