After just replacing 3 clutches on 3 ITA CRX Si race cars I determined that there are different sizes and will share my results. Please correct me if I'm wrong.
88/89 clutch discs are 7-7/8" in dia. 90/91 are 8-3/8". 88 will only fit 88 because of different splines between the 88 and 89/90/91. The flywheels/clutch plates are also different sizes too. 88/89 small and 90/91 large. Whole assemblies can be changed from 89/90/91. 89 assembly will fit 88 providing you use 88 disc.
88/89 clutch discs are 7-7/8" in dia. 90/91 are 8-3/8". 88 will only fit 88 because of different splines between the 88 and 89/90/91. The flywheels/clutch plates are also different sizes too. 88/89 small and 90/91 large. Whole assemblies can be changed from 89/90/91. 89 assembly will fit 88 providing you use 88 disc.