Market still isn't as good as it was 4-5 years ago. Yes a 400, 4-speed car will bring 2-3k more, but as stated above, only because there were a lot fewer made in 79'. The 403 cars a very good cars. Heck I've owned 2, 400, 4 speed cars, and my current 403 auto car has been the least troublesome to own. Never given me any problems.
Just don't give it away.