Lowering Possibilities???

[68-GTO]

Alright, i've been reading and trying to make a build plan for my car, i have a pretty good idea of what i want for my whole suspension. One thing i've noticed to be important for the entire build is ride height. I'm not really sure how to figure this out, i remember reading on a thread that Denny68 lowered his Elky 5" or so (with some modifications). I want between a 3-5" drop on my car, the lower the better but with minimal scrapage. I guess i'm wondering what kind of modifications are needed for say a 5" drop, for a '68 GTO?

Thanks for any help.