The car looks nice, as does the price. I think it just needs the EGR system cleaned. If I'm not mistaken, there were some performance parts for the 3.8 in the Mustang, so that might be an alternative to a V8 swap, if you want more power and subscribe to the "dance with the one what brung ya" philosophy. IMO the only thing that needs a Chevy V8 is a Chevy.
There are more old Fords running a SBC than are running Ford engines. That could be why they are still on the road. I agree, on this wagon it needs a good tune up.