If you install that bulb, you may want to consider using a relay to operate it.
70/80 watts for low/ high-beam, may cause you problems with the wiring and switch.
A 30 year old wiring harness, and small diameter wire just might not be up to the task.
I don't have a wiring diagram handy, but if memory serves me correct, the headlight is not protected by a fuse, and you are going to be drawing a few extra amps with this bulb.