The factory overall inner cable length should adjust fine. If it's loose at one end it is because either the throttle cable bracket is to far forward. Or the pedal assy is bent (unliklely). Who's bracket is it? I always make my own. The only issue with using a factory long cable like a 6 cylinder is you may hae to loop it a bit behind the left head. The relation ship between th einner length and the outer casing of all factory cables i ssimilar enough to allow adjustment. I can cut and weld it for you if you need. Get a measurement of where it needs to be. I'm in Waterford Mi. Just finished one for the turbo Duster project I'm working on.
Doug