Hello! Trying to find a book and it's driving me mad...

[Alh]

I read this book in the late 80s or maybe the 90s, my recollection is vague so please bear with me - a behaviour experiment, volunteers awake in a different body on a different world. Some have changed gender. Females horrified to discover they have to menstruate and give birth the tradional way (possibly this was some sort of technology advanced future experimenting in a 1950s environment). Set up as an assigned couple. Some sort of public dissent, possibly one of the women was attacked by male partner? Mob lynching outside a church? The 'world' is a circular recreation, town, farm land, at first idyllic but then sinister, there's a threat from somewhere and a character tries to escape (crashes a motor bike into a tunnel wall?) and discovers they're on a spaceship. I think there's a machine where they can back themselves up but OH says I'm combining two stories at that point. Anyway, story resolves and hero and heroine agree to find each other back in real life. One of the gender change characters decides to continue in the new gender. Not much to go on but it's driving me mad......