Sepp, I live in the desert where the temp can break 120 and had to be very careful about cooling when I added A/C to my '57 with a 235. I never had any issues with the OE fan until I added A/C.
Here are some my learnings that touch on some of your questions:
-I was not able to find a shroud that would fit. As stated above, the V8 shroud will not fit and I was not able to figure out a way to effectively adapt it. For a shroud to work properly, the tips of the fan blade must be about 1/2 exposed outside of the shroud with the other half inside, so the shroud would have to be very skinny to fit and work properly with a 235.
-Replaced the OE 4 blade fan with a 6 blade one of the same diameter. I was not able to find the optional GM version of this fan that was available for the TF trucks, so I used a repopped one. Send me a PM if you want the vendor info.
-Made sure that the radiator and the block were well flushed. I had some sludge blocking the drain outlet on the rear of the block under the #6 cylinder.
-Changed out the thermostat from a standard 180 degree to a 160 degree.
-I also added two electric pusher fans inside the grill tied to the A/C circuit, but this does not address your questions.
Matt
