On the quad-round setup for my '72 SE, I just used 110W aircraft landing lamps for the high beams, which are readily available in the correct size. I had to notch the headlamp buckets and upgrade the wiring, but they were way brighter than anything else available at the time, or since. Cheap, readily available, and illegal as hell (and a cop will know them instantly)... but I had hideaways, too. It's nice to be able to see road signs or deer eyes from half a mile out, particularly when you're travelling above the century mark for long stretches.