Haltech wire harness

Finding an inline variation of that vintage of a connector could be nearly impossible, but you could make your own by desoldering the connectors off of a donor ECU and soldering them to a perfboard, making your own break-out board.

A few years ago i did some disassembly of one and found that the FI connector was made by AMP, but the others i could not determine.

I can just use something like this and jump 2 pigtails together I would assume?

This seems like an option too. Obviously would have to figure out what the pin sizes are.

Yeah you could totally use jumpers into the Z31 harness plugs and then pot them in place, as long as like you said, pin diameter is correct and makes a good contact.