160-210 is the perfect temp for a motor to run at! The manifold will usually be pretty hot cause of the crossover. Are your manifolds aluminum? If so it would be really easy to open up the ports with a die grinder. If your motor ran any cooler than 160 I'd be restricting the water flow to get the temp up. Cold motors like to eat gas like it's cool. Not a whole lot of power either. I'd keep your setup just how it is. And to be sure nothings wrong, flush the block with a garden hose, exhaust water lines off. Just to be sure there's no sand in the block.