WingCmdr
M60A3 or A5?
NBC is whole nother issue, and I do not believe there is any turret pressurization on any American vehicle in the '80s and possibly to this day. Look at the preparations for Desert Storm.
(I actually feel the Soviets installed it to show readiness, but in reality I would not trust over-pressurization to work on vehicles in a combat environment with armor no thicker than your average SUV door.)
My unit in Germany went from M60A3s to M1s. The NBC system was a filtration system that would filter the air and you would hook your M25 gas mask to it before the gas mask filter. No A5, A3 AS I STATED.
M25 Tank Gas Mask
The M25 / M25A1 chemical-biological masks are special masks for crews of armored vehicles. These masks protect against chemical and biological attack in the form of vapor or aerosol agents when hooked to the vehicle filtered air system or when used alone.
https://olive-drab.com/od_soldiers_gear_gasmask_m25.php