Anyone know what this gas tank is out of?

Hard to see but it has a 6 screw and cork gasket, brass float sender with nothing but provision for the sending unit and a pickup line which had a sock on it. vent I think too, the nearby grommet to the sender unit is a small opening, i suspect for a roll over valve... possibly, then there is a single large opening which is visible for the filler neck.  
It also had slimy black sludge inside, diesel maybe..?    The sending unit looks like the kind GM used, Jeep used I think, way back.  

Not much for numbers or markings on it.  

I still don't know, but since it was made in '74 it would obviously have been in something made after that.  Ford used some plastic tanks back then, but there should be a Ford ID# on it somewhere if it is one of theirs.

Chemplex appears to be a company that produces fuel additives but i couldnt find anything about tanks.  The 74 makes sense if you account for the screws in the sender and then how its setup. however, I wonder if its not a diesel tank, I am only basing that on the fact there is no filler neck vent, which i realize could be internal to the neck ,but then it makes me wonder what the bushing on top is meant for.   it appears ot be a saddle, that takes 2-3 straps.  I was thinking maybe a heavier duty truck, maybe aftermarket add on tank.

Sometime in the late 70s gas tanks got federal legislations that required them to have identifying stampings that meet criteria, so I think this is pre that.