Credit: DPR Pentax Forum OP zakaria
From this roughly to-scale drawing, putting aside the small perspective and other scaling errors, I do agree that the estimated filter thread is in 67mm. When compared to the FA 20 F2.8 lens which also had a 67mm front thread, the sensible guess of the maximum aperture of the new lens would be F2.8, too. It should not be a re-packaged FA 20 as the new lens is much longer, nonetheless. Good. ;-)