Lyc O-235 How much room needed between mags and firewall to remove mags

Hello folks. My kitplane manufacturer is ready to fabricate my engine
mount and the Lycoming O-235 I have chosen is near the weight limits
that my plane can handle. I am trying to find the answers to two
questions:

1. The distance needed between the mags and the firewall to be able to
remove the mags for service without having to remove the engine?

2. The published length, by Lycoming, of the O-235 is 29.05 inches.
I have been trying to locate a dimensioned drawing to verify if this
measurement includes the mags. Does anyone know where to locate such a
drawing or know how else I can verify that information?

Thanks. Don...