There is a bit of information you can extract from this TCDS (JT8D-219) if you know one additional detail:
The tachometer drives on older-vintage engines are all of a spec that says when the drive pad turns 4200 rpm, the steam gage reads 100%.
From the TCDS, the N1 tach pad is turning at 0.511 times fan rotor RPM. Thus when the pad turns 4200, the fan turns 4200/0.511 = 8219 rpm. This represents 100% on the N1 gage.
Similarly when the core turns 4200/0.343 = 12245 rpm, that's 100% on the N2.
I don't think many newer engines use the old-style tachometer system in this illustration, though...