1988 RX7 SE with red injectors?
 

I have a 88 rx7 SE.... and the injector guide at rotary resurrection says it comes with the purple high impedence injectors.... but mine were red?

and how do you go about testing the impedence of the injectors with an ohmmeter?

Yes, use an ohm meter. As a guide if it si higher than 9 then it is high impedance.
I think (not 100% sure) that early 88 had low impedance and late 88 had high impedance

do I use the two terminals on the injectors?

And the date of manufacture specifically is 10/1988

You should have the High Impedance injectors. I have the same set in my own 88se and they are high impedance, you can tell the difference between teh lows because they have an offset plug slot whereas teh earlier years had the slot in the center(the lil thing that slides into the harness plug)

They are high as stated ^. Mazda changed to high imp in JAN of 1987
Low imp is 2 to 3 OHMs and high is 12 to 13 OHMs