The group you were raised in sounds interesting (and somewhat familiar) to me. I was raised Seventh Day Adventist, and at the time it embraced many of the social restrictions that you noted. SDA doctrine is not truly Fundamentalist in the technical sense, but it can be very conservative (although it does range between ultra-conservative to liberal within the denomination).
I was raised in a very conservative congregation that Ive observed liberalize somewhat over the years (I no longer attend, but much of my extended family does, and listening to them over the years has kept me abreast of some things).
I earned BA and MA in History, with a personal interest in how eschatological beliefs have influenced human behavior; or, stated another way, how does what groups believe about the future cause them to act in the present.
This interest was sparked by my experience as an SDA, a group with a well defined and prominent eschatology.
The Gospel Hall Brethren sounds like an interesting group to me. Do they issue any publications, or statements of belief?
Again, thank you for sharing such a personal story. Im very happy that you were able to maintain a close relationship with your parents after leaving the group. Sadly, this is not always the case.