The dimensions of the original Guild 449? case must have changed. The original early 90s case was supplied with the GX model. I do not have a circa 1990 case to verify. But the newer cases, including the new Guild Bluesbird cases, do not work well with the GX. The headstock, ( cake knife), is a bit too long and the neck angle is not right. It may work fine with Bluesbirds, Songbirds, etc. with a snakehead type headstock.
maybe someone with a GX model will advise whether the GX fit in the original 1990 case. And possible the difference in the original case that made it function correctly for the GX.