The plastic parts that you will find in the bottom of your oil pan and maybe stuck in the oil pick-up screen will be from your cam timing gear and the valve oil seals... A very smart thing to do on these motors is put a high quality roller chain timing gear set-up...The good ones start at about $80, if it is cheaper than that its not the good one... I would look on ebay or go to MTS.. MTS sell everything for these motors...
Automobile(s): 1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
Re: 472 Internal parts
The timing gear is usually aluminum center with plastic teeth. Over time, this sector either wears down or starts to crack and seperate. Then your ignition timing becomes comprimised. The broken teeth fall into the pan and get sucked into the oil screen. Same with the oil seals. Exposure to the engines heat will cause the seals to harden, crack, fall out of position, and find their way to the pan with the return oil flow. With the seals gone, your engine will start using more oil because the excess oil will find it's way past the valves on the intake stroke. This causes the carbon build - up on your cylinders, and spark plugs. There is some plastic used on your distributor, but it wouldn't find it's way to your oil pan.
This is why we suggest replacing the timing set with an all metal timing set. The double roller type stands up to engine torque better than the single solid gear set, and as the 472, 500 and 425 are torque monsters, the double roller is assurance of longevity.