[Bored&Stroked]

The problem with a definitive answer is that the only one that is accurate is "it depends".

Having higher compression is a big benefit in a flathead for normal off-the-line performance, cruising a hotrod around town, etc.. Flow becomes much more important at higher RPMs - which very few flatheads will ever see on the street.

Also, consider that compression has a LOT to do with the overall bore/stroke and cubic inches. You pick up a lot of compression in a big cube engine - without doing anything to the head at all - it is all based on the size of the cylinder you're filling and how far it travels up on the compression stroke before you hit TDC. Your engine is on the smaller side - 276 cubic inches - so you'll need to keep the chambers smaller than you would on a 304" plus flathead.

For what you're building, compression will be your best friend. It is a lot cheaper to chase compression than it is to experiment with max flow. Which takes years of experience, dyno work, track work, lots of parts, etc. To achieve higher flow potentials, you get into heavily ported blocks, big valves, special chamber work, etc -- and what works for one engine combination may not be right for another. Also, in order to USE all that port work, valves, etc - you need a lot of flow from your carbs and manifold. How many carbs do you plan to run and which ones?

Also, squish/quench is a big deal on any flathead. You'll want to achieve about .040 to .045 above the pistons as your final clearance dimension (with a head-gasket on). Most head-gaskets are about .050 to .052" thick - so factor that into your measurements.

In the end, unless you're looking for sustained higher RPMs and max high-RPM horsepower, you're better off keeping the compression high and putting flow as a secondary concern.