I'm going to run a hilux diff in my van, when i put the sr20det in.What ratio's should i use,i bought a 4.3 diff but i think it will be too tall. Also i'm thinking of running a four link rear set up.That Smka sells has anyone used them for road use.

A 4.3 won't be too tall.. in fact may be too short. But just check your getting the terms the right way around.
The bigger the number the shorter the ratio will be. 
 
For a turbo car taller ratios tend to work better due to the increased torque. You don't want to be changing gear so quick when you have just come on boost. Would just be a waste of that useable power. Short ratios are used for high revving NA engines so they can stay in the power band.
 
I have a hilux diff there. I can see what ratio it has which may help you? As 4.3 will be fine for my NA engine. Ill check next time I'm down. But most hilux diffs do tend to be on the shorter side of things..
 
4 link isn't really required for a road car. Its more for track where fine tuning of axle location is needed. 
For a road car, a good set of leaf springs like a few use with the extra rebound leaf, and good shocks like Bilstiens. Id put in a panhard or adjustable watts to locate the sideways axle movement as well. If after all that you are still getting tramp.. perhaps some trailing arms. But if leaf springs are done right you probably won't need them.

Ill be using 3.7 diff gears in my Hilux diff, which was the same in my KE30 Corolla, with a GT3071 on the SR20,
 
I have a 6 link in my Mk1 Cortina, which will be driven on the streets, I went this way, as i knew down the track i would have dropped the leaves and tighten up the rear end, just figured do it once, and do it right, i can still run leaves, and wider tyres also, here are some pics with the Hilux diff, as you can tell not really anything off the shelf and had to be made to suit
 

 

 

 

 
Hope that gives you an idea

I'm guessing you will be using the SR20 5-speed also. 4.3 in my opinion would be too short. My 180SX has a 4.083 and takes off like a shower of **** but there is very little room for high speeds. All depends on what kind of driving experience your looking for on the road.

Thanks guys,love that set up but i think a 6 link would be to much for my van