Got it all done and it worked out great, the 2x8 beams are plenty. All we had to by were the 2x8's, we reused all other lumber so it only cost about $25. Thanks for the help, we got all of our "storage" stuff off the ground. I'm really glad we went with 4' deep and not 8'. We would have had to buy all the lumber new, and it would have been too deep to use. This worked perfect and was just big enough. Oh, and a couple tapcons into the block and it's extremely solid.
I did something very similar to this in my outdoor shed. It is 12x10 and I used 2x6's at 24" on center to run the 10' span across the shed. I then laid 3/4" plywood on it and hung an attic access ladder. It came out great and serves nearly the same identical purpose you are using yours for.