The reason there is neck dive in 335s and SGs is not because of the neck to body weight distribution, but because of the strap button location. If you look closely, you'll notice that the strap is able to pivot on the button (behind the neck) making it feel 'neck heavy' there are a few solutions to this;
1) Wear the guitar higher
I know I know, It's a very personal thing, but these guitars were not meant to be worn the modern low rider way. they were supposed to be worn close to the chest, locking them in place.
2) get a different strap
a) a leather strap will stick to you better than a nylon one will
b) a strap with eyelets will grip down onto your shoulder better
c) get a weighted strap to counteract the balance
3) relocate the strap button to the upper horn. Lots of players do this (Iommi, BJ Armstrong). Just be sure to drill the hole before you put the screw in.
Good Luck!