Cast iron intake water passage rust on fresh rebuild...

[Wishmeluck]

I have a rebuilt 351w flat tappet I had broke in a few months ago and has been sitting on the stand since. I'm finally coming back around to getting it ready to install and when I took the t-stat housing off to put the thermostat in there's now surface rust in the cast iron intake water passage from the builder running freshwater through the engine during break-in to keep it cool and I'm not sure what to do. Is this normal and something I can just flush after running a bit and it'll be fine? Or do I need to take off the intake and have it sandblasted (again)?
Thanks...

 

[Tiha]

You can flush it with water, get most of it out.

If you want it shinny new you can try a radiator flush, but I am not sure they make very good ones anymore. Not as caustic as they used to be.

But honestly, it won't hurt a thing. Fill it with a good antifreeze mix and run it. You will never know the difference. It won't create any problems.