Quite simply, there isn't one!
If you indeed have an "old Stash" of Portriga, i.e. before 1988 then you have been treated to some of the finest enlarging paper ever made. The micro-contrast in the shadow areas is second to none!
In 1988 Agfa was forced to make a "minor change" to the emulsion, they removed the Cadmium due to its manufacturing impact on the environment. There is a long story that goes with this and subsequent warm tone papers not worth going into here.
I once did an ad campaign for Agfa and took my fee in Portriga Rapid, fortunately I still have some of the pre 1988 paper and will continue to use it sparingly. Chloro-Bromide papers such as Portriga tend to have better keeping properties when frozen than ordinary Bromide papers.
I have tried many papers since and of the papers which still remain in production that Bergger graded Warm Tone and Ilford Multicontrast Warm Tone Fiber Base to be as close to my liking as is currently available.
I use GAF 135 developer, which is a warm tone developer mixed from scratch, I try to keep my developing times to less than 1 minute and use Potassium Bromide as a restrainer if needed, generally speaking these tricks will enhance the warmth of most enlarging papers.
That said, no trickery is needed with the older Portriga, out of the box it is a glorious enlarging paper!