Well,other than air shocks,or coil overs,shock absorbers are not designed to "hold up" the rear of the car.That is what the springs are for.If you are using Caltracs,I would suggest getting a set of the monoleaf springs he sells.If you call him he can set you up on ride hieght.
I know it's probably not what you want to hear,but it is what I would recommend.