Are you talking about the original fabic insert top, or has your roof been filled with sheet metal?
The originals are tacked to the wood framework.
If it's metal it's glued on, just like most late '60's to early '80's OEM vehicles. Any competent upholstery shop should be able to do it. If they don't know how, run, run, run away from them and find someone who knows what they're doing in the business.