I think the Radius V is an improvement because it uses an external V-clamp technology. Less to go wrong.
There are some who think the original Radius is better ever since Dahon altered the design to mill away less crucial material. However, the basic design is unchanged and all of the deficiencies have been retained.
Maybe ThorUSA could sell you a Radius V. Definitely contact him - he is totally trustworthy and his prices have always been very reasonable. Thor disagrees with me about the Radius issue. Besides that, he will be able to give far better expert advice than me of what can be done. For example, he might be able to confirm if a Dahon post will be able to be installed.
It may be an option to alter the top of your Tern post to accept a Revolve stem. Cut off the top, make a stress relief slot, add a seatpost clamp of the right size, slide in the revolve section and you're done. There will be some things to beware of, I don't know if the diameters of the Tern stempost is suitable for the above mod, and even if the are, the Revolve stem has a system to prevent it from rotating in the bottom section of post, which will be absent in a self-mod. Unless you are mechanically able enough to add such a feature.
Last edited by jur; 08-28-14 at 09:18 PM.