How to clean cooling system???

[Fostang]

I opened my radiator cap today because last night it started dripping a little water and wanted to check if I had sufficient coolant and too my surprise it had a lot of sludge in their. It's definatly oil in my coolant but no water is going to my oil. Therefore I have decided to change the heads again but wanted to know what the best way to clean out the coolant system was?? I really do not want to put it back together with all that residue in their. Is there anything I can buy or will simply flushing the coolant system several times help??? I really don't think it's a gastket problem my thought is that one of the heads is cracked somewhere and it's the passenger side one. Any ideas of what I can do will be greatly appreciated. I've nothing but problems since I put these heads on. First car wouldn't idle right then when that was fixed it smells extremly rich but plugs are white also the smell isn't comming from the exhaust big mistery to me where from. Now there is oil in the cooling system.

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67'fastback-Edelbrock carb,intake,cam,valve springs.Rhode lifters, CompCam rocker arms, windage tray,cerama coated headers,dual flows with H-pipe, modded c-4,tci stall converter,perma cool electric fan,aluminum water pump,griffen aluminum radiator,accel 8.8 cable,wide cap distriburator,magnetic pick up,v-matic hurst shifter,edelbrock performer nitrous, carter electric fuel pump,ignitor coil,solid motor mounts,magna racing suspension,poly urathane bushings,under rider traction bars, comp. eng. s