Getting started to work on my 1974 Dart Sport. I got questions

OK, so it has a 340 under the hood, not original, but a definite upgrade, probably has an 8.25 rear axle in it, unless that was chucked in favor of an 8.75, another upgrade, but we don't know what trans is in it. Check your VIN number, paying attention to the 5th character, if it's a letter 'L', the car was born with a 360, if it's a letter 'G', it was born with a 318, or a letter 'C' would be a slant 6.