There are different lengths but the 75 and earlier cars that use the clutch pedal pulley need one designed for that style. I have some for that style that are 60" long if needed.
The pictured NOS cable listed on ebay has a part # of 355592. The Napa part in the link above is listed as 61.91 inches but is not listed for a '73 Vega. The RockAuto part-http://www.rockauto.com/catalog/moreinfo.php?pk=65093&cc=1062032&jnid=468&jpid=0-lists a length of 54.25 and is supposed to interchange with GM # 355592. Is either one of these the right cable?