If I remember the glide input shaft can pull all the way out just like some of the older Fords like the C4 and C6 transmissions.
You might have just pulled it out to where the unworn bushing area on the shaft is, and that's why it stopped at 1.5 inches instead of coming all the way out.
Also if IRC you check the endplay on the output shaft of a glide instead of on the input shaft.
Like I said though, it's been a long time and I could have that confused with any number of other transmissions.
Maybe a Youtube vid would help answer some of those questions.