I have ridden the Pista and liked it. With the Pista and probably the others you will need to change the gearing (It is very tall for street) and add a brake. I know the Pista fork is drilled for the brake.
You will enjoy the process of sourcing up the used stuff to build one from scratch tho. It is silly, but I really have a lot of pride in the old bike I ressurected and I feel it every time I happen to turn and see it hanging up at work or take it out for a spin.