Always dislike drilling holes in the SS Firewall and especially fabricating doublers to mount stuff. But, otherwise it makes it more difficult to maintain in the future. (Although in this case the holder should never have to be removed/replaced.) Just loosen and replace the ANL fuse, and (the failed alternator).
Anyway, it's time consuming to do all this detail. Will have to terminate the wire ends, and torque the nuts ... but after the shrikwrap is added to the crimped terminations.
