Iran/Persia in the WWII period had quite limited local heavy industry - the ability to produce heavy construction equipment, rails and other materials for rail expansion, locomotives, rail cars, etc was minimal to nil. Other than fuel to run vehicles, everything used to expand the infrastructure in Iran had to be imported, and step one was improving the infrastructure at Iranian ports to handle the increased traffic. To accelerate this you need to make that decision, redirect current manufactured goods from where they were going to Iran, and rearrange factory priorities to make that stuff instead of other stuff. You also need to direct manpower to Iran from other places to actually do this, engineering units are in high demand and taking recruits and training them to be useful in these units is longer than cranking out infantrymen. The minimal lag time between the Allies (basically the USA) making the decision to do this, and significant amounts of stuff and people arriving at an Iranian port is 4-6 months, producing results at any significant level double that time.
Now answer the question, with the stuff you are sending to Iran, units you are sending to Iran, and some factories that are producing for that effort instead of something else, what are you not doing?
Now answer the question, with the stuff you are sending to Iran, units you are sending to Iran, and some factories that are producing for that effort instead of something else, what are you not doing?