727s had 2 different size converters, 11" and 12"; smaller is high stall, bigger is low stall. If LS stands for Low Stall it's gonna stall pretty low behind a 318/5.2, like 1700 rpm or less. Which is fine if the engine is stock but if you change the cam it will definitely want a higher stall speed.
Both 727s and 904s got lock-up converters in the late 70s. They can't be interchanged with non-lock-up converters and have to be matched to lock-up transmissions. There is a way to tell the two types of transmissions apart but I don't remember what it is of the top of my head, something with the input shaft iirc.