It might be that the tailpeice was mounted a bit off centre, and then the saddle slots were filed a bit off centre for the strings to run straight down the neck. ??? Don't know if current production saddles will be a good fit in a '78 bridge. You might have to get a complete brid ge w/ saddles if you want to correct it. But be aware that if you correct this so that strings are centred on the saddles, if the strings run straight down the neck today they might not do that after the fix.
I don't think that the strings being a little off-line from the pole pieces will have any effect on sound.
Here you can see how my '79 was when I got it.
http://www.nationwideguitars.com/1979ri ... kerlh.html
The saddle slots were pretty much centred, but the tailpiece itself was so off centre that you can see the strings are not running straight down the neck. I moved the whole tailpiece to correct this.
Also, you can see that the pickguard is mounted a bit low (not pushed all the way up against the surround for bridge pickup) resulting in the neck pickup being way off centre (compared to the bottom of the neck).
For me, none of these "problems" had much/any impact on sound and playability, except the G string getting a bit close to the edge down the neck. For me it was mostly an aesthetical issue, especially looking at how the ran down the neck.