Heads fit but takes custom y-bridge, pushrods, few other things to even work. Then you're missing out on the largest gains of the L5P platform, the cylinder head flow improvements.
I believe the LBZ/LMM ECMs can be modified to use the OEM L5P reluctor wheel, I do not know if anyone has tried with an E60 controller.
Following in the event that someone has, I know we've not messed with any L5P swaps yet.