Timing Chain in Monaro - When?

[Yanayaya]

Despite the paper work my Monaro came with and the work I have done since, I have no true histroy about the timing chain, it's age or if it was ever replaced. My question is when do you typically replace them? How hard are they to change? and is it worth upgrading the timing chain and sprocket to an uprated one as I have noticed a few options out there.