I don't want to sound like a smarty pants, but often a modified car may not yield the % increase in power it could because acuratetuning can yield the very last degree, but a poor tune can loose most of the gains!
You must check out MustangSix's post on power from the Engine Analyser 3.0.
The headers only give a 15 to 25% boost if the carburator is big enough and tuned to suit. The 32/36 is an easy 130 hp carb with its stock 25/26 venturis. If you go up to 30/31 venturis, you can gain another 15% if you have the large1.75" post 1970'/80's head.
A 280 degree cam, with the right bits, can make a huge increase as the engine is so undercammed stock.
Worst impairment to peak power is the single drink 'baud rate'. If it had 2, 3 or six point dispensing, those sharp turns and in the log manifold wouldn't be such an issue. Power is a fucntion of torque times a speed factor. Power is improved when the rate of fuel flow is improved. Jack sumed it up in the post he made a while back. Unless you do an Offy, 2-bbl Schendahl, or Mustang Geezer-type direct mod, you won't gain lots of power.
The 2v head has with it a better exhast, intake and carb, and bolts on another 35 rear wheel hp. Without cam.
A log with a good 32/36, headers, exhast and a GOOD cam should match a stock 2V mod everywhere.