I don't know how anyone could install a barrel on an '03 without at least opening and retracting the bolt! On a 98 Mauser perhaps, but on an '03??
The use of draw lines made barrel replacement in the field easier, but its main purpose was to allow the barrel to have the sight bases installed and the extractor cut made in barrel manufacture, whether the barrel was destined for a new rifle or for use as a replacement barrel.
The 98 Mauser, since its extractor did not fit into the barrel, could just be screwed in and torqued down, then the sights installed and the final headspacing done.
(FWIW,, the system used at Springfield was also used on another gun which had to have an extractor cut made before the barrel was installed - the Luger. Quite a few Luger "experts" have come up with fanciful explanations as to how those draw lines were used, usually involving barrel removal and replacement, sometimes more than once!)
Jim