Kinda hard to tell what you're referring to there. Is it the stuff on the gasket face or the stuff in the port? Either way, all needs to be removed before putting it on your motor.
Could it be crud/corrosion in the coolant system? Looks like thats one of the water passages isn't it. My original intake had a little bit of build up that looked similar to that in the water passages when I pulled it off.
Looks like corrosion (aluminum oxide plus glycol (antifreeze)) from not using corrosion-inhibiting antifreeze. Is this on the front of the intake or the back? If it's on the back and it's not a passageway, make sure there are no pinholes in the intake before using it. If it's on the front, how on earth did the engine stay cool?
that is on the rear of the manifold. is that a performer rpm air gap? My 351w edel one doesn't have a crossover in back, so the water is just stagnant. its not that big a deal. you do need to clean the gasket material off and whatnot
My engine came with a Performer RPM with a similar build-up in the back coolant passages. Looked to me like someone had put it there though, it's feels kinda tough for an anti-freeze build-up though.
What size engine was it on, 289/302? I'm just thinking that maybe if it was and it had 351 heads at one time that the gasket mismatch to the intake part of the passage could have been restricted and that's why everything got trapped and gunked up like that.
most ford intakes don't have a rear water crossover and if you don't use the correct type of antifreeze this is what will happen. it's corrosion and obviously it's a bad thing. another thing you can do besides running the correct antifreeze with a corrosion inhibitor is to use a radiator cap with a sacrificial anode, the coolant will attack the anode instead of the aluminum in the engine. i've used these and they work quite well.