Only few of them are worth to convert, since are quite old (and already converted from other sims).
You need anyway the original 3d from the author of the conversion, otherwise it's not possible to do it.

Our A1-Ring is an evolution of that version, but we had to work a lot on it, to improve it and to bring it up to standard. Maybe was even easier to convert it from an other, more recent, version.

Namie tracks, can be even used in nkpro, but will have some problems with the transparencies. In some of the tracks it's acceptable since objects without transparencies are really far away.

We did some early experiments in 2009, when the track editor wasn't public yet,using the namie tracks bringing them online creating manually the grid with 1000 of attemps (old days in which we were desperate to add new tracks )
A1-Ring
Phillip Island