Lookin' good! Ya I believe 8" base is generally the rule in these things. Those look like nice beefy pedestals btw. 
I agree, the fwd'n aft adjustment feature is nice. (There are days when I feel tall and then some when I feel short ...?) Just make sure when you slide the seat back'n swivel it, it don't bang into the gunnal or control.
Nice job so far. Cain't wait to see the finished product.
Carry on.