I have both spec of these cabs cars and the engines are the same, both have Injection, both are 1.8 8v, both have 5 speed gearbox's, both have MFA dash,the exterior on Gli should have single headlamp grill with chromed surround, side trim and sill trim chromed, GLI - is small bumper car, and GLI was from 79-83 only. The interior are only a little different lesser spec seats than GTI.
GLI has the better exhaust manifold over the GTI as it has the 6 bolt 2 downpipe exhaust - much better than the GTI/Clipper round two clips manifold single downpipe.
Hope this helps.