Here is the switch you need.
http://www.napaonline.com/Search/Detail.aspx?R=MPEOP6626SB_0213430147The oil gallery you need to access runs down the driver's side of the engine with a 1/8" pipe thread adapter for the oil pressure gauge installed in it just to the rear of the exhaust pipe area about 4" above the oil pan rail. Remove the adapter and install a short 1/8" pipe thread nipple into the block and a 1/8" pipe "T" fitting. Connect the oil pressure line fitting into one side of the T, and screw the switch into the other port. Run a wire from the ignition switch terminal that supplies voltage to the coil to one of the connectors on the switch that is parallel to the other one. Run a second wire from the switch to the choke coil, leaving the center connector of the switch with nothing connected to it. This connector can be used to ground an idiot light, but that's a subject for another "basic wiring 101" course.
Jerry