Hi llgillette and Welcome to the Forum!
The tag axle shocks will definitely be different. The tag axle was installed by the coach builder (National) not the chassis maker (I assume Ford here) so there is no parts commonality.
The tag axle is probably made by Dexter with a Mor-Ryde suspension. Mor-Ryde should be able to help you determine the correct shocks.
Mor-Ryde