Timing Chain Guides

Greetings,
I am new to this forum and have a question re: 79 450SLC

I read somewhere that there are plastic guides that are positioned against the timing chain inside the front of the engine and that these should be periodically replaced to avoid internal damage.
Is this a "do it yourself" type of operation or must it be performed by the dealer.
Would welcome any and all input on the degree of difficulty and any tips on this task.
Thank you in advance.
Kurt Bunting