How do ya drop the rear of a C20 with leafs 2"?

[MrC1]

Sorry for the barrage of questions!

I know there's lots of threads about this, but I couldn't find this specific answer.

I've got a '72 C20 with leaf rear suspension (HD option?) Anyway, I want to leave the ride height stock for now, 'cept I'd like to drop the rear 2" to level it out. How's this done? Are there 2" longer shackles available? If so, where?

It appears that 2" longer shackles might not quite fit under the bed, but I'm not sure. It's a fleetside metal bed, BTW.