Ported box for Type R 12?

I recently got an Alpine SWR-1221D (300 rms). I have a sealed box that's 1.57 ft^3, and a Pioneer amp that'll give it 250 rms. I was looking at just taking the sealed box I have since I took a while to build it to fit perfectly in my pickup, and just porting it, and using the Type R in it. Looking at the specs, it shows ported volumes should range between 0.75-1.75 cubic feet. Ideally, I'd make it as big as they recommend making it. But it would be a pain to remake the box since I won't have this truck for a whole lot longer. So, my questions are: Is there any reason I shouldn't just use this box? If not, what should I tune the port to, and is there an advantage to putting two ports instead of just one? Also, will there be any downside to having the ports on the side of the box instead of on the front?

The sub's behind the passenger seat of my Tacoma. So the port would be facing my seat.

Also, any idea what I'd want to tune the port to?