Welcome!
Please understand that the 1966 440 TNT was upgraded for 1967 and later model years.
The original 440 TNT was named for "dual snorkel" air cleaner and "dual exhaust", but still had the normal 440 256/260 cam, normal exh manifolds, and normal 1.60" exh valves. As in "Twin snorkels" 'N "Twin pipes".
The 440 TNTs in 1967 and later had the upgraded 440 HP cam (new that year) and 1.74" exhaust valves, with the also new 440HP upswept exhaust manifolds. WITH the trademark dual snorkel air cleaner and factory dual exhausts.
The 440 TNT option was not specific to 300s, but could be ordered on other Chryslers, including Town & Country wagons.
Enjoy!
CBODY67