Longer leaf spring shackles to lower 72 C10 anybody used these?

[tll74]

I want to lower my 72 C10 with rear leaf springs 4 inches. So, my plan is to use a 2 inch longer shackle and dearch the springs 2 inches. Does this longer shackle clear the box floor? Anybody have any experience, sujjestions and or input to keep me pointed in the right direction??