I was discussing this with JimmyInkedUp last week.
T4 converts to T3 at a rate of about 25%. So 150mcg of T4 daily will give you around 32.5mcg of T3 daily. And if I recall, the body produces approximately 25mcg daily if T3. So should be enough to see some results.
I'm in the same situation, I have a large cheap supply of T4 available, but T3 is hard to get.
Hope this helps.