You are running a 326, the seat pressures will allow you to run without seats or additive.

If you were running a 326 HO or 350 HO with a high gear and mainly 3-3500 rpm freeway driving, I would say maybe.

I have torn down many a set of Pontiac heads at the shop and maybe 5 out of a 100 pair had noticable seat recession.

Installed seat pressures of 175 (closed) and 400 plus (open) to see accelerated recession on most Pontiac heads. If it has not happened by now (40 years) likely it will not. You see accelerated seat recession with roller cams and lifts of .600 plus.

My opinion? Save your money..If the heads need a rebuild, have them installed. If not, leave them alone. I would use Ferrea 5000 series valves, Comp Cams springs, locks and retainers.

SERDI cut seats.

I can get you the installed height and seat pressures if you need.