As Leon says, exhaust mods are a good place to start. Either a Corvette manifold, or have your factory manifold split. Fenton headers look cool, but they were made for full out racing applications. They won't yield positive results unless you plan on running your 235 around 5000 rpm.

The next place I would turn would be the cam. While there are some who would recommend a reproduced Howards or something similar, I would recommend a stock cam from the 261 truck engine. This cam is a solid lifter cam and it is actually the same grind that Chevy ran in the '54 Corvette. Plus, the last time I priced one, the 261 cam was about 1/2 the price of a vintage repo.

An upgraded ignition system would also help. There are a couple of routes to take here. A nice vintage type dual point set-up or an HEI set-up. I went for the HEI and have enjoyed it so far.

After these mods is when I would recommend the dual carb intake. This happens to be where I am. I am in the process of gathering parts.

You will get a lot of different opinions on this subject. There are several different vintage publications available that can help show how it was done 60 years ago when the 235 was still new. I would suggest reading some and developing a plan that will work for your application.

-Tim
'51 Chevy 3104 w/'56 235, 848 Head, HEI Dizzy, Corvette Cam, Split Manifold and Dual Carter YF's