I just had some disc brakes(Baer 13"), put on my 67Chevelle SS..they feel much better ofcourse...Originally my mechanic said the booster wasn't neccesary..
It's definetly hard to come to a complete wheel stop, but maybe that's normal.
thoughts
p-

You are the one who has to make the call. It's impossible to say if your brakes are acceptable or not without driving it.

IMO, if you find it difficult to stop the car, it's not safe to drive. Install a booster.