True all of the above. All full scale aircraft must have firewalls that meet certain fire resistance and containment standards and most often the firewall is a full bulkhead where the radial or beam type engine mounts protrude forward in to the cowling area.

In the case of our model aircraft there is no real effort at fire resistance or containment made however the in the same way as a full scale aircraft the bulkhead from which the radial mount (or standoffs) attaches or the beam mounts protrude forward is called and considered the 'firewall'.

John