anyone know an easy way of caluculating the amount of lift achieved from various lengths of springs. Basically I need longer leafs for my '83 but want to keep the same ride height.The springs I have are too short due to the add a leaf the prev owner put in & shackle angles suck.I would guess a 2-3" lift is where Im at now. Is there anything that swaps in for this kind of lift? what kind of chevy springs fit?

For about 2-3" of lift you could try older (late '80s/early '90s?) Mazda 2wd springs. Or try 63" Chevy springs from an '88 to '98 truck (I think those are the right years). Most people who run these setups use some extra leaves or blocks to get more lift.

To use either of these springs you'll need to weld on some new front spring hangers (farther forward from stock) and most likely new rear shackle hangers.

I've seen a web page with leaf spring calculations on it, but unless you know the exact steel properties and what not, its better off just to get some junk spring packs and start playing. Pull them apart, turn them upside down and stand on the leaves, measure the deflection. Compile a table of the spring rates and lengths and then put together a pack and give it a try. If you need more or less lift, add or subtract leaves or swap siffer for softer leaves, etc. Repeat until you get the height and ride you are looking for. That's how I did a few packs I have run on my truck.