Hello I would just add my thought having been in a similar dilemma recently. I am in the fortunate position of having a lovely original '59 Beetle: this is unrestored largely, only two previous owners and very 'original.' I picked it up as a 'hobby' car to tinker with, keep in the garage, preserve, restore gradually , drive locally and take to an odd 'meeting.' I also have a wife and 7 year old daughter. As a compromise I have fitted a single (hide-able) lap belt for my daughter in the middle rear... emphasising that I will only very rarely use this for short journeys and it is 'easy to tuck out of sight keeping the original look of the car. I also very carefully drilled and welded the plates underneath the body so that if I want ti drill out the welds in the future it will be easy. This solution has kept my wife happy for the very few miles I take my daughter out for a ride.

I guess i am lucky though because i have a separate modern daily driver and a '73 Beetle which has a much safer set up than the '59. This i would use for a spin on any longer distance or dodgy conditions/nigh-time etc.: It's not just the seat belts, the lighting is better (12v, and 'visibility' of all lights especially from the rear), the handling is better, (wheels tyres etc. and chassis set up), the speed is better, (less likely to get smacked in the rear going uphill), vision outwards is better, (bigger windows).

I would also say that if like me you have spent 30 odd years driving with a seatbelt, it feels most odd at first without one as a driver, and I think that many feel very insecure without the reassuring restriction of a belt! Driving an unbelted car with 34 hp and limited braking with old style tyres really makes you more aware as a driver, especially about speed. Perhaps all learners should have to do it! I am sure we have all been passed by kids/OAPs bombing around in overpowered modern cars for the most part unaware of the huge amount of energy such speeds generate (is it 'kinetic?') The old seatbelt giving them false confidence in their own or others safety!