Hi Alfraser, the short answer is no, there were no restrictions concerning Catholic marriages in Scotland at that time.
As for the "rush job", it was quite normal, although even at that time couples who had a child before 9 months of marriage were still being chastised by the kirk session.
My maternal great grandparents were strict Church of Scotland and yet 3 out of their 4 daughters married into the Catholic church. (The other daughter never married).
Regards,
Lodger.