I used one of those magnetic heaters for many winters on my old '75 450SE. I attached it to a piece of aluminum conduit so it would be easier to 'stick' it to the oil pan each evening, and remove in the AM. I also wrapped the battery with a 'battery blanket' heater, plugged into the same extension on a timer.
I recall looking into one of those in-line coolant heaters, that mount in the radiator hose, but could never get around the issue of having the interior heater 'on' as it had the auto climate control.
If you do decide to have a block heater installed, be super careful of the old freeze plug that will have to be removed to put it in...real easy to chip a piece of the block around the edge, and it'll never seal right.

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1986 560SL
2002 Toyota Camry
1993 Lexus