The leads are copper so the resistance is close enough to zero, however the ends plugs (the plug ends) should be between 900 and 1100 ohms. If they are Beru then the ohmage is actually printed on them (at least they are on mine). The distributor cap also has built in resistance. Check this cap and the rotor and make sure they are good. Dissy caps are known to develop small cracks in them so clean it out well and do a very close inspection.

There is a DYI sticky on this forum that shows how to change out the valve seals. If you have upwards of 120,000 miles (180,000 km's plus) and then depending on the use of vehicle, the valve seals are in line for replacement. If the car has been left for long periods between runs the seals can dry out so (this can explain why M103 engines with relatively low mileage seals require replacing - previous owners include little old ladies who only drive the car to church on Sundays or once a month).

If you have upward of 160,000 miles on the engine it's time for a head pressure test. Possibly valve seals, stems and head gasket are due. Although this is a little expensive if you intend on keeping the car for a few years this would be money well spent.