Creating this thread for anyone who may be interested in installing a bigger oil cooler (and perhaps filtration element).
Maktrans in Poland offers these adapters for Volvo specifically, as well as other applications of the gearbox here.
Volvo literature does not specify direction of flow for the oil cooler, so attached is a photo of the adapter, the port closest to the engine is the outlet.

I intend on removing the old heat exchanger using a piece of tubing.