Anyone install a 1974? leaf spring rear end in their 1967 GMC/Chevy

[sduckworth13]

I bought a 1974? Chevy 1/2 ton truck suspension with 5 lug, front disc and rear drums , actually I believe the correct year is a 1976 Chevy 1/2 ton. I am planning on swapping the rear end in my 1967 GMC 3/4 that has a 14 bolt with 8 lugs, drum brakes and leaf springs on it and installing the later year 12 bolt, 5 lug and it has the 3.40 ratio rear end. Has anyone done this swap before. I just had the 1974 suspension sandblasted and I believe I'm going to need to get the perches moved in 3/4 of a inch so I'm waiting to paint it. I'm using the leaf springs from my 1967 3/4 ton for now or will I want to change them too because I'm doing a 4/6 drop. I read that the 3.40 ratio 12 bolt was the first year for the 3.40 ratio rear end in Chevy trucks. I'm wondering if someone has some pointers on the swap.