It's not a straight forward drop and bolt in job despite the same body and chasis. After the engine, there's the electronic conversion. Then there's the new HVAC that has to be outfitted. Finally when the front end is done, the tranny needs to be swapped to get the gear ratios to match the power output of the engine. In between those major items, there's a whack load of little things that needs attention as you go along.
I considered converting m44 to 3.0 once but ended up buying the M3 instead because it was just plain less expensive.