I changed my heater core today and...?

I am planning on installing a new radiator and all hoses. I am also going to have someone change the water pump and flush the cooling system out. It's all original on a 96 F150 with over 260K miles, so I figure it's all due. So anyways, my question is does it matter when I have it flushed? I would like to change the radiator and hoses before I take it to the shop but I don't want all the stuff from the engine getting in the new radiator and hoses. I haven't actually hooked the heater core into the system yet. The last time it was flushed was about 5 years ago.

Thanks.
I changed my heater core today and...?
If I were doing this in my garage, I would unhook the old radiator, and use the old hoses to flush the engine block out seperately. Then I would replace the water pump, put the new radiator in, then replace all the hoses and hook up the new heater core. Fill with coolant/antifreeze and would be on my way. Good luck.
I changed my heater core today and...?
FLUSH IT FIRST, THEN WHEN YOU REPLACE ALL THAT STUFF,YOU'LL BE STARTING WITH A CLEAN SYSTEM.
flush first
if you are changing the radiator, new water pump and hoses. there really isnt much to clean out. the block doesnt hold the little stuff, like the heater core and radiator cores do. dont think it would be of much use to do it after that is all intalled new.