Well that is a bit of a problem. Then if that's the case either between a 347 short block with the factory stock heads or a factory short block with aftermarket head, intake, and turbo...
The factory heads and intake will not flow near enough for the 347. You'd probably wouldn't pick up much until they are swapped out. But it could be built now to handle whatever you'd plan to do in the future.
The most gains then would come from the H,C,I, and Turbo swap in that case. But you'll be limited with the stock block and rotating assembly.
Also don't forget to factor in the extra price for a larger fuel pump and injectors and the requisite tuning that would be required.