As a pure guess.. I would suggest the cams that might have been added would have been the US spec M3 cams as this seems to be a fairly common mod for the M52.. With the cams and the shrick manifold you'd be looking at pretty decent power levels to be fair (I would imagine somewhere in the region of 230-250 bhp (fly)) based on other cars I've seen with similar mods - I've also updated the flow rates for various intake manifolds below:
Flow figures for the manifolds (CFM per runner):
M52 manifold is 180 CFM
M50 manifold is 280 CFM
Schrick manifold is 240 CFM
Schrick manifold, extrude honed is 318 CFM
It would probably be worth sticking it on the rollers to see how it's running and what power it's making..