The irregular verbs of the Spanish (Castilian) and Portuguese language are very similar, but we also see differences. In the table below I put some of these differing forms side by side.
|andar 1||anduve||anduvo||andar 1||andei||andou|
|ser, ir||fui||fue||ser, ir||fui||foi|
The verb “andar” is regular en Portuguese but irregular in Spanish.
In Spanish, the first person of the perfect often ends in -e while the third person form has -o. In Portuguese however the first and third person conjugations are equal.
Where Spanish has “j” (this is [x] phonetically), there is often an “x” in Portuguese. Although mostly a written “x” sounds the same as “ch” ([S] phonetically), this is not the case with these verbs: for example “trouxe” sound as if it were “trousse”.
In the conjugation of “dizer” they indeed even write “disse”. Could it be that in old documents, this was written “dixe”? I think I have seen examples of this.
And in fact they do exist, as becomes clear from this Googles search: +dixe site://purl.pt.