Why not use what he used. I recently was looking through some old issues of Darkroom Photography,(May 89), that had an interview with Gibson. He stated at that time he was using Tri-X rated anywhere from 100-1000ASA on the same roll,depending on the image, developed in Rodinal 1-25 and printed using a Leitz-Focomat C-1 enlarger.(posted 8087 days ago)Gibson discussed that he would usually print on a grade 3 or 4 paper and if he needed anything higher, would overexpose and underdevlop the print.
He also printed mostly 11x14 and occasionaly 16x 20 at that time. These enlargements would also lead to emphasized grain in the images.
This info predates a great deal of his work but would include some of his better known images from Somnambulist (1970); Deja Vu (73); and Days at Sea (75).