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I think the 98 GLTs use the 13G turbo and the T5s use the 16T. the 13 has less flow but faster spool up. You'd need to check the flange (ie the G has the angled flange like the 850s - not sure what the T5 used in 98). The first question is what are you looking to do with the change?
Just swap one for the other, my boy blew his engine in his(vin 56), and he's buying one with a blown turbo(vin 53), and wants to put the good one in that car.