Definitely!
More money spent, sure. Although if you’re doing TTI’s and a full exhaust maybe not that much more money depending on the current fuel system set up and FI conversion used.
But fuel injection would be the best way to improve fuel economy, assuming you’re already tuned correctly and don’t have some kind of engine problem that’s hurting mileage. For a driver it also has some nice advantages beyond the best mileage you’re going to get. No warm up time like with a carb, which makes it easier to drive all the time and improves your gas mileage (not sitting around idling with the choke on). In theory, more accurate tuning, which again helps the mpg’s but also might improve drive-ability, especially if the current tune isn’t quite right. Should be less fuel smell too, although some people like the “old car smell” that definitely includes some unburned fuel.
Stage 1 cam? Ok. Doesn’t mean anything to me without specs or a part number.
Recently rebuilt doesn’t mean it’s properly tuned either, or that it doesn’t have an issue. Less than 1,000 miles might actually worsen fuel mileage a little, engines loosen up a little as they break in, so less friction loss compared to brand new. That’s a small difference though.
And what kind of fuel mileage are you actually getting?
Which one? I’ve got a couple extra exhaust manifolds.
Headers can improve efficiency a bit, but that usually translates to more power, not better mileage. And with a mild 318 it won’t be much power either...