Santucci's book is written for the late model sixes, not the old 235.
Your best improvement is to get a 261. But, the 235 will do since you have it.
Full race cam
Cast Fenton headers
New intake and carbs, dual Holley Webers are a decent setup
Electronic ignition
Balance the engine
Shave and port the head, 848 head is highest compression.
I'm sure I missed something. Here's some shot's of my friends 261, it's around 250 hp.
http://myoldtruck.com/gallery/showimage.php?i=2660&c=500&userid=238
