340/360 exhaust manifolds
With those casting dates I would say yes, they are originally off a 340 but '73 340 and '74 360 will interchange and function the same.
The casting date usually precedes the car's build date by about 2 months or so, and they built 340 Dart Sports and Dusters until the third week in July of '73.
Then they started producing the 360 cars in August some time.
