I have over the past year had 3 different engines in my Black Horse Travel Air. On each engine installation I have had a different orientation for the set up. I have had to re-drill the firewall to acomplish this and have filled/glued each old hole with dowl so not to weaken the firewall. I have now installed yet another engine and its orientation is "normal" i.e. head at the top. I have had to lower the engine mount because I can't get the tank any higher.

Is the Thrust Line a vertical line through the centre of the firewall or a horizontal line??

Can I mount the engine too low on the firewall and will this adversely affect my plane?? (The pre cut hole in the firewall is roughly the centre of the mount).

Does it really matter??