http://www.injectorservices.com/injectflow.htm notes that part number 195500-1370 is used by Denso for both of their low- and high-resistance 550 cc/min injectors. Be sure to measure injector resistance before installation.
Below is some information sent to me by Rod Hiorns (Thanks, Rod!).
Mazda RX7 tan top Denso 550 injectors are low resistance with a center notch in the electrical connector.
Mazda RX7 purple top 550 injectors are high resistance with an offset notch on the electrical connector.
Both of these 550 injectors are marked 195500-1370.
I guess the bottom line is be sure of what injector you are installing in your engine!