the only way to tell flow rate is have them flowed! we get brand new injectors that flow diffrent rates from time to time when we test them so second hand ones can have flow rates all over the shop. 210cc is pretty common found on alot of cars. its bigger than 300cc thats harder to find. on our boosted race engines we use 1200cc and on a nat asp 6 litre we use 850cc. just get new 210cc ones. ring me on tue there about $130 each from memory could be even cheaper.
mick