3 Series Engine The Same As The 5?

I read this is the 5 series buying guide: "Sadly
for some reason the M52 can pop its head gasket, if the car doesnt over
heat then you should get away with the head being pressure
tested/skimmed and new gasket(have £800 in hand and you should be ok!),
If its over heated,throw the engine away, from experiance the heads can
crack, However so can the block!. The alloy block sadly warps with the
head which means stripping the whole block down skim it. Fear not your
problems have not ended yet! If your block hasnt warped you will find
that when you come to tighten down the Cylinder head the Threads in the
block have a habbit of stripping which then need a few helicoils to fix
this." Are the 3 series engines the same? Do they all have alloy blocks? I was thinking about buying an N46, but if a late E36 comes along at the right price and condition, then I might get one of those.