I have not seen a turbocharger kit anywhere for an I-6. I think you are on your own to make one work. Although the pistons are cast, they're very thick. So if you keep your boost to a low enough level, not more than 6 or 7 psi, the cast pistons will probably live a long time. As far as the rods and mains are concerned, they're more sensitive to high rpms than increased torque. So if you size the turbocharger so that it makes its power between 2000 and 4000 rpm, you won't really be dealing with too high of an rpm. The mild cam grind will keep you from going much higher than 3500 rpm anyway.
The T03 turbo that was commonly used in 80's Chrysler 2.2 engines would work very well. You could tap off of the remote oil filter lines to provide oil to the turbo, and gravity return back to the tank. The water lines would come from the lines to the heater core. And it would mount just below the exhaust manifold.
The most work would be making the adapter for the exhaust manifold and the hat for the top of the carb. It might possibly require moving the alternator to the other side, so some bracket fabrication would be needed. But all in all, I don't think it would be that hard.
What might be easier is mounting a centrifugal supercharger on the passenger side of the engine. Then all you're doing is adapting it to the carb. If I had a supercharger handy, I'd go that route. But I have spare turbochargers lying around from my Shelby Charger days.
A 6 psi system would probably only get the 235 up to around 200 hp, but the torque improvement might be up in the 300 lb-ft range. And aside from the premium pump gas requirement, the cost to superturbocharge an inline six is relatively low, as long as you keep the boost under control.
They already come with 8:1 compression, which is very compatible to forced induction.
I got about 230,000 miles off of a Dodge 2.2 liter turbo-4 and it only had cast pistons!
