[fesler]

We do them both ways it really is up to what you are looking to see when finished, some people like the look of seeing the bulk head on the firewall and some don’t. I personally think they look good both ways and like you said if you have an issue they are much easier to work on when mounted on the firewall. I have been doing Vintage Air for more than 10 years now and have not had many issues with the fitting so either way will be fine just depends on the overall look you want.
here are some samples for you