On my 67 frame, there are 2 sets of holes at the lower control arm mount.

Why was that? Does it make a difference to ride height?

The arms were found bolted through the upper holes.

Are you talking about the rear suspension, lower control arm, forward mount?  If so, mine (69 & 70) just have one place to bolt in to.

Yes, sorry, the rear lower mount,

hmmm, mine only had 1 set of holes.   The nut is a bit awkward to get a wrench on, and while I was tightening the bolt with a socket the wrench pulled off the nut and I got the box-end of the wrench in the eye.  I'm still sporting a bit of a black eye from 4 days ago.

Clint, That's why GM designed that the nut be inconveniently located. It's to poke you in the eye for attempting to work on it! 

Actually, I figured out a while back that you need a good quality offset 15/15 box wrench to get on that nut proper.

Oh, and I love how GM pre-mounted the UCA's to the frame mounts, with the bolts facing inward! You have to remove the mount to pull the arm. The bolt cannot be slid out otherwise.

Anyway, what affect would it have to move the bolt to the lower hole?

Would it raise or lower the ride height ?

I can't get it straight in my mind. But I'd actually like to see the car 1/2" higher at the back. The new arms have a perch that is 1/4" higher, so I need another quarter.

Cheers,

If you are looking for halve inch raise, I would try it first the way it is. It is not a one to one ratio. I added a halve inch spacer under the spring and the ride height increased a whole inch. If you're wondering, I needed to level the car out after replacing the front springs. I forgot to mention my control arms are mounted to the lower holes.