I am restoring a Vienna Regulator that had no pendulum, weights, etc. I need some guidance on selecting the proper suspension spring for a pendulum. Seems there are many sizes available with really minor differences. I suspect one too stiff will stop the clock after a short time. In this case, I am restoring a GB regulator with 64 cm pendulum. I am a little confused as to the proper relationship between the suspension spring and the bob weight. Any good advise from the pros?