I used stainless steel machine bolts to mount mine and put some rubber grommets between the regulator and fender.
As to whether it is supposed to be vertical or horizonatal, I have no idea. The regulator on my jeep was mounted vertical, but my replacements from Walcks were made to be mounted horizontal with the terminals pointing down. I used one of my existing holes but had to drill two new ones..

I put some more SS bolts in the remaining holes to make them pretty
