Commercial sporting rifle .303 headspace gauges are for SAAMI limits, the Milspec headspace limits are more generous. The rifle may be safe to fire with milspec ammunition, and possibly safe with most sporting ammo.
Since the .303 headspaces on the rim milspec ammo with thicker rims than commonly found on sporting ammo takes up the slack.
If headspace is on the loose side, over .068 but under .074, it should be safe to fire but cases likely won't be suited to reloading.
A milsurp rifle isn't easily judged by commercial specifications.
When the Lee Enfields left the factory headspace would have been no more than .067 but wear , sandy environments, and degraded milspec ammo increased the headspace over time.
That said the rod under the upper band ID's this as a Turkish Drill rifle, and it may not have been in good condition when passed on to the Turks.
Anything over .074 headspace is taking a chance, and a wallowed out chamber coupled with loose headspace could make one dangerous to fire.
I'd strap it to a tire and fire several rounds of both milspec and sporting ammo, then check the fired cases for bulges.
As for bolt heads, a good condition bolthead with a low number may be longer than a hard used bolthead with a higher number.
Unless you want to put some work in the rifle you may as well sell it off at a reasonable price, then look around for one in better shape.
Or you could look for a sporterized No.4 with unaltered barrel and strip this one for parts to restore that rifle to milspec.
From the look of the bolt track this is a No.4 MkI as opposed to the MkI*, which is a point in its favor.