with most early celica's containing an 18r, the crossmember curves to the front of the car requiring the sump bulge to be more rear facing.
a front sump 18rg puts the bulge at the front, ironically the same configuration as celica's with 2t's in them as on the t series celica's the crossmember curves towards the rear.
this allows you to put an 18rg into a t series celica (or to find a rear facing crossmember with power steering attached for your r series celica which is what i was going to investigate....but missed out )