Agreed that you'd need higher capacity, as such, I'd personally go with at least a 120A unit. Doubling the capacity rating in this case is a safer bet.
Also, reviewing my old school notes and noting there are a few ways to skin a cat, .......Method below (sorry no pretty pictures embedded) also allow you to switch in and out each/both/all house and start batts for backup use to start engine in the event your start batt craps out. Also allowing you to shut off all batts entirely to all sources........
Side noting also that a solid state Isolator (Or'ing diode) as compared to the mechanical relay's in ACR's/DVSR's gains you the ability to NOT have to parallel a charged battery with a dis-charged battery in order to charge it/them.
Each battery can draw (charge at will as needed) what it needs, when it needs with no chance of back charging (dis-charging) one batt into another especially during higher current in-rush/alt voltage sag while paralleling/connecting a fully charged batt to a not so charged/dead'ish batt.......Sorta provides you a Duracell analogy of "never mix good battery's with bad battery's" by nature eh.
ACR and DVSR and the like are also are mechanical contacts (relay's) that arc and burn and wear over time (highest arcing/wearing during high inrush currents during initial paralleling), A diode Iso of course is a solid state device and if spec in correctly (using a 120 Amp model w a 60 Amp alt) will typical run 10's and 20's of years if not more.
All just a personal preference I'd have and have had in the past with your type of set up and that has worked very well for me and what I prefer...........Also, you could bump that alt up too, if inclined BUT, the Iso would have to come up as well.