Help! I need to identify my upper control arms please! 70 dart.

OP has Kelsey-Hayes SBP discs, so standard small ball joint UCAs.
Being a slant 6 has no bearing on the fact that it has disc brakes, they were an option available with any engine.
Don't know of anybody offering new or repro small ball joint upper control arms, so a wanted ad would be your best bet. And don't worry about welding the ball joints in, it's common practice to give them a couple of tack welds to hold them in.