New guy...probably old question!!

[Canadac10]

Hi, new to the forum and new to old trucks!! Just bought a 1970 C-10 longbed. While the body needs some love the frame and mechanicals are mint. Last owner replaced all of the suspension, but with stock components and stock height. First thing I want to do is drop it and after combing this site and others there is a ton of info our there...almost confused lol
My question is how much drop can you go without doing a frame notch in the rear?
And who are you having the best luck with kits? Again, so many companies to pick from. Will be converting to disk brakes on the front at the same time.
Thanks for any info and sorry if asking an old question again!!