bulbs are easy to replace, but take care with the wattage. the old k2 runs a 75/55w, but that is the limit for it. 100w was too much for the electrics, let alone the reflector.too hot. the problem in old bikes is the general condition of the harness, with connections the main faults. careful dressing of the bullet connectors with fine wet & dry paper- all mating surfaces- will help you will find the biggest gain for least $$$ here. protect the connectios from corossion. tape stops electrical contact, not moisture. spray on lanolin is the best protcector i've seen so far for waterproofing electrics in a motorcycle application. it is made from wool grease, a sorta kiwi k.y. it works for many things. ask a kiwi.
high wattage equals high load, and may not leave enough to charge the battery, if you use the headlight a lot. \