Theres an easy way to find out if the injectors are low or high impedance. Just hook a multimeter up and check the resistance. (ohms) High impedance is usually around 12 ohms and low impedance is usually under 5 ohms.
This won't tell you the size though. But generally high impedance is 550cc and under the exception being FD secondaries which are 850, or bored out secondaries which can be 1200 and 1300cc.
I did find this chart. Not sure how accurate it is but
Here
I removed all the other car types and put only the information for RX-7's.
Based on the post above mine I made another chart. So basically just look at the color and take a guess on what you want it to be haha.
