I have never had any difficulty locking up the wheels and skidding the tires any time I want with my stock brakes. I don't know what power assisting would do for that. But, it's exactly that - locking up the wheels - that could only be improved by ABS which I've never heard added to a 40's stock car. But, I don't drive 75 on the freeways and never have been inclined to "compete" with modern cars. I drive in the far right "slow" lane between 60-65, even when the speed limit's 80! I always seem to have plenty of company going my speed in that lane. At night I add a few magnetic reflectors on the back for extra visibility.
I know. Each has their own safety comfort level. I sometimes have passengers that are uncomfortable riding without seat belts (so I put them in) but I wouldn't ride a motorcycle without a helmet when old Chuckles up the street, who has a car just like mine, rides his Harley all over the town and country without one. I figure my stock '47, even missing many of the modern safety features, is still safer than his Harley, even if he did wear a helmet. I don't sky dive or hang glide either. So, there you have it - each to his own way.