Iron Clad;
The 261 is a great engine and if I had a 235 and a 261 and was looking to install an engine in a new project then I'd certainly pick the 261. However, you stated you have a good, low mileage 235 and are looking for some bolt-on HP - right? Keep in mind that a stock 261 was rated at 150 hp while a "stock" Corvette 235 put out 155 hp. As far as I know the Corvette got that hp with carburation and dual exhaust and without the benefit of an "848" head.
You asked about dual exhaust - in the great McGurk article that Tim linked to, on his first test after running his baseline, he added a Corvette manifold and a 2nd truck muffler. That raised the HP number by 6hp at 3000 rpm. Now, I'm not saying you'd get exactly that increase on a 235 but I would think it would be somewhere in the ballpark. I'm guessing a set of Fenton headers flow about the same as the Corvette manifold did, maybe better. Oh, and IMO you don't need anything larger than 2" exhaust piping. The next test was with the addition of dual carbs. An additional 11 hp was added.
So, by bolting on carbs and dual exhaust they gained 17 hp.
You can get a Fenton or Offy manifold from Tom Langdon and the carbs that match it.
Another easy bolt-on is an HEI ignition. I like the one Tom Langdon sells. I think with those 3 "bolt-ons" you'll achieve your goal. Now, add an "848" head, and a one of Patrick's street cams later on and the ol' 235 will be puttin' a smile on your face for sure.
