I could be wrong and I believe shocks were not installed as original equipment for leaf springs. With the change to torsion spring axle that is still in use today was the addition of shocks included in the design of Airstream trailers. With that being said, if you want to install shocks then just a traditional type would be my recommendation. No gas and no added spring on the shock.
If you are looking to improve ride height because the existing leaf springs are not doing the job, then new leaf springs are what is necessary.
1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!