Different manufacturers often use their own plugs, newer plugs often differ from older ones so it can be difficult to find parts that fit.
Block heaters (coolant) are of two types; one that is bolted to the block and heats it and the other type has a heat element inside the block (in the coolant ducts). What type to use depends on the casting of the block (open deck blocks usually needs the first type).
Some more info about heaters should be found here:
http://www.defa.com/heating.php3?lang=