88 HF 1819 Hollow front sway bar, no bumper supports, no side impact beams, smaller gas tank, stamped rear LCAs, not as much interior, chassis mounted seat belts, smaller axles 13" steelies
88 Si 2011 Rear Sway Bar, Sunroof, Rear Wiper, A/C, stamped rear LCAs, chassis mounted seat belts, alloy wheels 14"
88 DX 1922 stamped rear LCAs, chassis mounted seat belts
89 HF 1834 Hollow front sway bar, no bumper supports, no side impact beams, smaller gas tank, cast rear LCAs, not as much interior, chassis mounted seat belts, smaller axles 13" Steelies
89 Si 2138

Rear Sway Bar, Sunroof, Rear Wiper, A/C, cast rear LCAs, Door mounted seat belts, Alloy wheels 14"
89 DX 2048 cast rear LCAs, Door mounted seat belts, rear wiper
90-91 HF 1967 Hollow front sway bar, no bumper supports, smaller gas tank, stamped rear LCAs, not as much interior, door mounted seat belts, smaller axles 13" Steelies
90-91 Si 2174 Rear Sway Bar, Sunroof, Rear Wiper, A/C, cast rear LCAs, Door mounted seat belts, disc rear brakes, alloy wheels 14"
90-91 DX 2103 cast rear LCAs, Door mounted seat belts, rear wiper
This is all the differences to my knowledge. Of I'm wrong on any of them please correct me.