Do i have to lift the rear shocks or do any kind of adjustments to install 20 inch rims in the rear?

84 El Camino Conquista

That my Man, would depend on what Tire you mount to the Rim, and the depth / width of the rim. (but either way, it would NOT be the Shocks you would have to change)
:dontknow:

whats the widest i can go to try and have less modifications to do?. i wana go with very low profile tires

That would still have to be determined by the type and condition of your rear suspension, Rim off set, ect. It may just be to your advantage to visit a Tire / Rim store and inquire as to what your opptions are, and there are too many variables to get into here. Figure out what you want, THEN find out if it will work.

alright.thanks man

Spend an hour at a Tire store, you'll thank me for it.
You don't want to spend a $1,000 plus to find out they won't work. And what works on some one else's, may not work on yours.