it will definitely help, but if it isnt growing by AAS i doubt you gna see that much of a difference, start off your shoulder day with rear delts, i got mine by putting bench on incline, lying face towards bench, and doing rear delt flyes with dummbels, keeping elbows out, really blew my rear delts up, also train them on back day... Look up shoulder flossing aswell, will help bring your shoulders back to bring out rear delts more aswell
like this but bend elbows more, and use much heavier weight lol
definitely look up shoulder flossing, brought my shoulders back ALOT and stopped the crackling and shit i was hearing
I know you wanted advice on igf-1, but since its so expensive i dont know why you wouldnt be willing to try something new first