I've had IMA do some work on my '76 2.0 a few years back (like 5 years ago). Any "good" shop has 1 old guy who remembers working on these cars 20 years ago.. but not too many of those guys still exist.
I would try Chapman, IMA (Chantilly), ASG and Autobahn as they are some of the more established Porsche shops near you.
RPM down in Newington. Some folks use a shop closer to Baltimore.. GT Racing maybe? Tiffs? can't quite remember the names.
Arm and Leg? I'd expect $150/hr or more rates at any of the independents. Not sure if there is a guy in Leesburg proper anymore. I know there is a shop that does Alfas, but not sure if hes a general "foreign car" specialist.
The shop you chose may also be dependant upon the type of work you need.. Carb work? FI work? Suspension work? Rust repair? Interiors? For some of that, there might be non Porsche specific shops that can do just as good of work..
Or, as Beat Navy mentions, any number of folks on the board here might be local enough to help you out, provided food and drink is provided