Truck Forums - head or intake gasket? chevy

Another newbie here. this question pertains to my 1990 chevy silverado with the 5.7. i am trying to determine which gasket problem i have(intake or head). it has 150,000 miles and has always run great. about a year ago i lost my power steering pump pulley 18 miles from home(deep in the woods). i drove it home and it did get very hot. its winter in Michigan but it overheated the other night in just 1 mile when cold(gauge pegged all the way right). pulling the oil dipstick revealed about 3 inches of muddy looking coolant ABOVE the fill line and a half empty radiator. i pulled the intake and a mechanic friend looked at the old gaskets and believes that they failed in the back corner where the block off plate was, due to a little light colored goo and some leakage of oily thick goo just inside under that corner. he belives there is about an 80 percent sure that the intake gasket is the problem but i dont want to put it all back together and find out its a head gasket but i cant really afford a $500.00 bill right now either. any help is greatly appreciated. thanks, Mike.