Good grief Adam, a 6.9 needs to stay a 6.9 and there is no shortage of engines for them (I have one for sale on CL right now for $650 and there's another fellow down the road that's selling one for around that price too).
If you want to mess around, there are plenty of W116's to do a similar conversion to.
I bet that the oil filter housing can be transplanted from the older 4.5 M117 to the new one, but personally, as I have an oil extractor, I'd rather pull the battery tray and get it from the top.