[Jeron]

Some block heaters heat the oil dierectly but most heat the coolant and therefore passively heat the oil.

I think the coolant block heaters can get to well over 140 degrees, depending on conditions and size. Some come with switches to keep the temp from getting too hot.

Apparently the drain plug idea is a no go because most heaters are too large and hence use the freeze plug area. I've found some magnetic type heaters and also some lower heater hose types. The lower hose type seems the most feasible.