I would think the concern would be whether there is sufficeint thickness at the chamber end of the barrel for a gunsmith to safely drill and tap for a scope mount. Another question I would ask a gunsmith is regarding the metal that the receiver is made of. On my 12 ga. Mod 66, it appears to be like "pot metal". It seems to be very light and as far as appearances go, doesn't lend itself to being strong enough to handle slugs. I cannot back this up with any scientific info, its just my observation.
I also checked the Weaver scope mount chart (available on their website) and they do not list a scope mount for the Mod 66, so you would have to find an existing one that matches the contour of the barrel.
You may want to consider a New England Firearms 20 ga. Tracker II. They are manufactured with adjustable sights and rifled barrels. The chamber is also thick enough for a gunsmith to D & T and NEF offers a scope base package with a hammer offset. Weaver also provides a scope base for it as well.
If you choose to stick with the Mod 66 project, choose a competant gunsmith.
Good Luck.
EVOC One
