How hard it is to install depends on the model. Mine have all had a threaded plug in the engine casting where I put the block heater. Hopefully yours does too.
If so, then comes the problem of unscrewing a bore plug that has been corroded in place for years to decades. I am told by people not to try it with the engine cold. Run it until everything is warm and then make sure your tools fit so that you don't ruin the head of the plug. Go slow, tap on it, use a hand impact driver, and be willing to give it a break until later....use all the tricks you know and it will come out.
Then just clean up the threads and screw in the block heater. I use a teflon thread sealing paste. The block heaters are very durable. I don't think I've ever had to replace one that quit.
Don't forget to replace the antifreeze that ran out when you removed the original plug.
Do not drill the bore plug to get it. There was an epic TBN post here a few years ago. I seem to recall that the cylinder sleeve wall is a lot closer to the back side of the plug than is expected. The heater installation job got a lot more complicated after that. But the OP was handy and got the motor back in it and running a few months later.