The key word is "restore". It won't be a restoration if you swap the tranny. Both of your options involve cuting a hole in the floor pan which would destroy the resale value. The least invasive would be an auto shift 4 speed overdrive, non computer control like a 700-R or a 200-R if you have the small bellhousing pattern. You can also adapt your BOP pattern to chevy if you need to. The Buick Electra estate wagons had BOP pattern RWD 200-R's and can be had cheap. I'd get the Buick collumn and linkage in a package deal with the tranny because you'll spend hundreds on custom linkage otherwise.