There are a bunch of SAS with leaf springs in the registry. Your problem is that 79' axle should have the wedgies and inner C's as one cast piece, which would make it hard to add leaf spring perches. Coil over shocks added a lot of work to mine. I thought it would be as easy as coils and shocks, but there is a lot of added figuring involved. And it was over 10K in parts alone.
I have had the Rancho 2.5" lift, 4" and 5.5" Superlifts, modified the Superlift to work better, and none of them was even close to the stability and flex I get out of my SAS. It drives/rides better on the pavement than it ever did and it has gone everywhere off-road I thought I should be taking it.
I always thought it would be fun to have something as beat as that Toyota looks to be just because I wouldn't care what happened to the body.