"...don't have the different sized boltheads to adjust headspace..." Yes, they do. They're just not numbered like the No. 4 bolt head. Therein lies the biggest problem if the headspace is bad. You need a handful of bolt heads to try with headspace guages until you find one that is ok. Gets expensive at $11.30US(Gunparts) each.
The bolt should close on a 'Go' guage(only used when installing a new barrel), but not on a 'No-Go'. However, if it does, you try a 'Field' guage. If the bolt doesn't close on a 'Field' guage, the headspace is on the high end, but still safe to shoot. 'Closed' means completely closed. If the bolt head is up, even a little, it's ok.