Fifty years ago the flathead was THE engine. I have owned and built many of them. While they are a fabulous looking engine and at the top of the nostagia list, as Dave S says, they are not cheap to build nor even particularly easy to work on. There are few machine shops that I would trust to build my $5000 (or probably more) dream engine as there are quite a few tricks to making them a viable and reliable powerplant. There is little chance that they will out perform any $3 to $5000 Ford or GM crate motor. You cannot, for instance, buy standard parts from Auto Zone or even NAPA. Bits and pieces are very expensive even on eBay. You can buy almost everything you need performance wise for a SB Ford or Chevy from Summit, Jegs or similar mail order supplier including a complete crate motor delivered to your home in 3 to 5 days.

What I'm trying to say - a Ford flathead, in today's world is for an experienced rodder/mechanic and is NOT the engine to start your rodding activities.