MUST READ THIS:
https://conceptzperformance.com/wiki/in ... l_Injector
ALSO THIS (if you have time and want to know more):
https://www.witchhunter.com/
The flow ratings page on witchhunter is a great resource for figuring out what injectors you have or what flow rating random injectors are.
Want to avoid headaches, ONLY buy OEM NISSAN or NISMO injectors
Since you have the original injectors out, confirm they are in fact original, you can do that with the stamping on the top, I don't remember what the factory number is so you'll have to do some research. If they are OEM send them to get cleaned and flow tested. s*** old OEM injectors are better than any of the garbage aftermarket or remanufactured units, bar none. Too many people have had too many issues with aftermarket injectors on these cars even in stock flow rates/sizes. If they are early redrills (phase 1.5) like described on the wiki (link above) then replace with OEM.
Here is where it gets really interesting, JECS is the OEM manufacturer for Nissan (inc. Nismo), as well as Power Enterprises, Tomei, and a few other high end performance brands. However JECS NEVER sold their oversize injectors to the open market for a LONG time so in the past any time you saw JECS on an injector larger than 370CC it was either a re-drill or a flat out lie. Recently it seems that the have started either selling to vendors their complete injectors or have made the endcaps available which is why you'll see them carried by Z1 and others in a plethora of sizes. Some have had good luck with aftermarket re-drill units but they are hit or miss and most tuners wont touch them. I haven't had the need to screw with injectors for a few years so I have no data on the new JECS units, word of warning, if you decide to go JECS make sure you buy from a reputable dealer, too many fakes and knockoffs out there along with old redrills mixed in with the new units.
In your situation the BEST thing to do is to buy a set of new OEMs from either CZP or SZ, then there is no gamble, you are guaranteed to have premium new parts built to OEM specs. This option is however the most expensive, about twice what you paid for the ones on Amazon. The other option is to get yourself a set of OEM refurbs from a respectable vendor or injector specialty shop, they will likely cost about what the Amazon wonders did but again you will get a flow test result and cert for each injector which will guarantee that you're getting the correct performance. In any case My suggestion is you send the ones you got on amazon back, get your refund and never purchase anything other than toilet paper and swiffer wet jet refills from amazon again.
In general stay the hell away from Amazon for any car parts, there have been thousands of reports of unscrupulous buyers purchasing real (expensive) name brand parts and returning garbage knock offs which then unbeknownst to the seller get put back into circulation. No one checks this stuff. Amazon is the new Ebay for Chinese knockoff garbage except Amazon cares even less, where as Ebay will 1 time out of 10 actually ban sellers for selling fakes, Amazon doesn't care.