Block off hose
 

I have an 86.5 Supra, non turbo, and can find nothing on how to replace a very short hose at the very back of the firewall near the heater inlet. Part of it is hidden betwen the back of the block and the firewall. Can it be replaced without removing the engine?

Yes it can, it has a spring clamp holding the little boot on so you need a pair of pliers to remove that then take the boot off and replace it with a new one.
Just make sure the engine is stone cold when you do it so you don't burn yourself.