You would be better off just buying a different frame with the looks you want. Chroming can be a can of worms if not done right, and the expense is not worth it in this case. The parts that you want to leave exposed will have to polished to a mirror finish, then the whole frame will be have to be plated.
A '78 Colnago is not a huge collectors bike at this time, but if it's nice original condition it would be worth more to keep it that way. Even properly restored bikes will be worth less than clean original finishes. When you start "customizing" to you own vision you will probably hurt the value even more.
But then again, it's your bike, and your money, so you can do it if you want.