What a bummer when restrictions are placed on modification to ones personal vintage car, another reason I'm thankful for living in the USA. (Other then the ridicules smog rules in California)............
Regarding the sway bars, if allowed, go with the I.E. 22mm front and back. Install the links on the front holes for the front bar.
For the rear sway bar, from the back of the bar to the backside of the link, 2-1/2", that's a good comfortable balance.
Good luck,
Salute'