Aluminium's rate of expansion (please note that there are heaps of ALLOY steels) is considerable. But rember, the alloy block engines use cast iron sleeves and the rate of thermal expansion is still kept safe enough that gaskets and seals stay in 1 piece. And if it is that bad, then the growth of the parts of the case that locate the shafts relative to each other, would cause enough change (and probably can) that the contact between the gears would change. In this case, both reduction (by temperature control) and restraint of the the thermal expansion should be considered.
High temperature resin would still be a good idea, to maintain stability. As would an alloy steel centre plate.
And as mentioned, CF is a pretty good thermal conductor and you should already have an external oil cooler by this stage.