Chevy Ky - My setup is similar to yours. I have a stock '49 radiator on a recently rebuilt '59 235. I'm using a 180F thermostat and a 7 psi cap. With this combination, the engine will run indefinitely at 185 degrees, even when it's 100F outside.
I would start by checking the size of your fan. About the time GM changed the 235 engine to full pressure (1954), they also increased the size of the fan. I'm told the pre-1954 fan is usually 16.5 inches in diameter. The fan on my '59 235 is 19-inches in diameter. This may not seem like a big difference, but a 19-inch fan pushes roughly 50% more air than a 16.5 inch fan at any given RPM. If you are using a smaller fan from an older 216 or early 235, it will probably have a hard time keeping your engine cool.
The larger fan also has a different bolt pattern than the smaller fan, so it's not a direct swap. I drilled new holes in my fan so that it would fit the bolt pattern on the short-shaft water pump. Good luck.
