Sorry for your loss, but congrats on inheriting a great system. The Vandees were the cat's meow in their era....way, way ahead of their time. Richard Vandersteen was a legend. I'd be surprised if you didn't think they sound pretty amazing. The BK amps were also top performing value amps in high end circles. Was he bi-amping with the two amps? I'm not familiar with the preamp.
At the very least, I'd hook up your Dad's system as a tribute, enjoy it for a while and get familiar with its sound signature, then decide how to implement it depending on your opinion of each of the components.