From a search of the forum there seems to be two throat lengths for the .264WM.

The original earlier factory throat which alowed projectiles to be seated out quite far and the SAMMI spec throat which is 'shorter'.

Have I got this right ?

I have bought an immaculate 1965 Remington 700 ADL with factory 24" S/S barrel. I can load 140 grain Woodleigh PPSN's out to 3.440" OAL with the projectile base level with the join of neck and shoulder of the case.

I have a Pac Nor SAMMI spec 26" super match C/M barrel ready to install once the accuracy wears off my factory barrel. Will it need the projectiles seated deeper ?

That's an easy one. Assuming you are right handed, hold the Pac Nor in your left hand, chamber end up. With your right hand, drop a loaded round into it's chamber. Press on it with your right hand to make sure it is seated. Then, turn the barrel upside down and see if the round will fall out on it's own. If it falls out without any help, then there is a good chance the throat will be at least long enough for that round.

Cheers.