Fox 351W power depending on build question

I am currently building a Lightning "Interceptor Bronco" based on 1995 intake and heads. This stock lightning combo with stock 8.8 compression ration made 240 hp.

Without a turbo or supercharger, I'm expecting 300 hp.

With only 91 octane fuel available, my target compression ration will need to stay below 10:1 compression.

Higher compression will require higher octane fuel. (or something inventive like water injection. Water has infinite octane.)

You will likely have too much compression with the Trickflow heads on 91 octane fuel.

You will need to carefully measure cylinder volume as well as cylinder head combustion chamber volume. You can get estimated intake manifold and cylinder head flow numbers by searching the net.

Once those are established, the remaining variables are: fuel management, ignition tuning, cam grind and compression.

You can lower compression by dishing pistons or boring. You can increase compression with domed pistons or shaved heads. Several gasket thicknesses are available.

400 hp is ambitious; but, you should consider a power adder: turbocharger, supercharger. It that case, you will want comparatively low compression to begin with.

You can also try plugging in the variables to software like VirtualEngine2000 and try to predict HP.