I having my shop tap the OEM M54 housing...like MasterC17 did. The main concern there is some possibility that there is a high RPM bypass built into the housing so unfiltered oil might pass through the cooler into the engine. I posted something about bypassing the OEM oil pressure sensor in a different thread but I misunderstood what my engine guy was talking about. So basically, he'll tap the M54 housing, install an inline thermostat and an inline filter. My engine guy and myself are NOT entirely sure about this so we're playing it safe. Plus, more oil filtering couldn't hurt.
Depending on how things go, the engine guy I use MIGHT...emphasize...MIGHT do this as a service. Put your name down if you are interested. Please specify if you just want the housing or if you want lines, cooler, stat, filter, etc...same setup as mine.
Be warned that if he does this, it won't happen anytime soon. I will HOPEFULLY test my setup 21/22 Apr if my car gets done. We'll log some oil temps, make adjustments if needed. Once things are good to go, I'll provide some details.
I will talk to him about a core exchange program. You pay for the tapping + core charge. You return a servicable housing...you get the core charge back.