Actually, you don't need an action block. Its a better idea to secure the receiver extension itself in a vise, rather than the receiver itself to prevent stressing or breaking the lower. 40 lbft doesn't sound like alot, but torsional stress isn't something the lower was designed to withstand.
As far as the wrench you are using, I'd ditch it. Tapco isn't exactly the greatest ever, but the tool you have should work as long as it's in spec. and has a provision for a ratchet at the end. Use one hand on the breaker bar or ratchet and one hand on the tool to prevent slippage. When reinstalling, use a torque wrench. I believe the spec is 40lbft, but check up on me. You can get away without torquing, but it'll give you the best results. Also watch out for the detent spring.