I'm on my second twin SBC boat- this one being a 28' AT with 350MagMPI/Bravos. The balance of this boat is much better than any 28 we looked at that was twin BBC equipped. We boat on the Great Lakes, and twins are a very good thing to have. If inland water is your only destination, a single BBC would fit the bill for a well-balanced boat in this length.
I'm not in agreement with the 'girly' sound of a pair of SBC's under the hatch- I've had more than one 'expert' tell me he loved the sound of those BBC's in my boat. ;) :)
Our next boat will most likely be twin OB powered- the fuel economy of the new HPDI engines is comparable to or better than SBC's, they meet the 2006 emissions mandate, and the reliability is there as well. Yamaha will have a new 300 hp model out by the end of the year.:cool:
Jim

Don't get me wrong on the outboards
 

I very much respect the performance, weight and reliability. That said, I want a family friendly transom and the sound I know and love (8 pistons, any size). I think outboards would be a little pricier too.

I considered custom SBC but I think I can Whipple a 350Magefi (takeouts etc available for 5k complete with a warranty) for the most bang for the buck, and I can run stock for a while first, then upgrade when i'm feeling spendy.

In this boat I would definately go custom twin SBC vs custom twin or any other BBC