I know your question is about the 235. But here is an article on the 261 that gives numbers.
http://www.selectric.org/55chevy/soup.html Kind of hard to read but it states that,
Stock 261 = 77 BHP at 2000 rpm
and torque= 201 pounds-feet at 2000 rpm.
With dual exhaust alone = 80 BHP at 2000 rpm
and torque of 210 at 2000 rpm.
With dual exhaust and a 2x1 with two Strombergs
= 89.3 BHP at 2000 rpm
and torque of 223 BHP at 2000 rpm.
What this does show is just by adding dual exhaust with free flowing mufflers and a 2x1 intake with Strombergs gave the 261 motor a
16% gain in HP at the low end of 2000 rpm and a
11% gain in torque at the low end of 2000 rpm.
And at 4000 rpm the gain was 21.5% in BHP over stock.
And an increase of 23% in torque over stock.
These are documented dyno numbers on the 261.
For a 235 I would think the percent numbers would be pretty close to the same numbers as the 261, give or take a small percent.
So dual exhaust with dual carburetors DOES add hp AND torque to these old Chevy sixes. A good 20% more at 4000 rpm.
It's not going to snap your neck, but only you can judge "Is it worth it" ??
For me the answer was "YES" it was for me.
