is there really no replacement for displacement?...

hi FABO, i've had my '70 swinger for almost a year now and she's absolutely wonderful. But she's only got the stock (yet extremely clean) 225 /6. i've always driven faster cars, and although the low end torque is nice, the high end torque simply doesn't exist. She's a brilliant engine, (she lasted 400 miles and back upto lake shasta a few weeks ago) but i really need to get some more power. Is it worth me getting a 2 barrel carb, header exhausts etc (and possibly even a turbocharger) or is it best just to find a 340 to throw in? i'm in no great rush, but if anyone has any opinion on the matter, that'd be great - thanks