Others are best at the math, though we have decided to mount a rooftop 24v AC unit on the cab which adds a 'new' 70a at max.
[@GeneralDisorder and I have had several conversations upon this and I understand his points well. If we find a complete RedDot Gen2 kitted unit I'd likely purchase it, though spending the time to source all the bits and pieces and installing the separate items, adding another idler to the main shaft just doesn't add up with my skill set and time available right now. Using an electric rooftop unit is not likely the best choice for most folks here.]
Since the cab and chassis need (and CAT specs) only two batteries we are splitting the four into two 2-series banks separated by a Victron Cyrix unit. That way the cab and chassis 2-series bank is maintained 'first' and the added accessory 2-series bank is maintained with the excess the cab and chassis bank does not draw. The Cyrix also allows the second bank to be used at start, if needed. This way we have a 'back up' bank of batteries with us at all times to run the main systems.
Maintaining four batteries with only a 100a alternator is likely fine when the batteries are fresh, though when they are drawn down significant our understanding is they bring us too close to the alternator's limit for the kind of travel we typically do.
I thought I had photos with a tape measure for the Neihoff, though not finding them. I believe it is a long J180 and the tabs are offset, not 180° from each other.
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We did need to modify the bracket and add a rigid upper arm. The original length serpentine works without adjusting the tension pulley.
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@MatthewWBailey went with a pad mount and I like that idea very much.
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Hopefully that helps—