Headlight bulb conversion

There are a few companies that offer a headlight conversion for our '64-'70 Chevelles and Camino's that replace the stock 5" headlight with a new one that has removeavle and replaceable bulbs. You have to use like a H4 lightbulb or something in that nature.

I've seen them at swap meets, but havent had any luck with finding them searching through the internet. Any links or help would be great!