Ford ,Chevy,exc.Parts in your mopar

Ive been reading about lots of guys putting Ford and Chevy parts (Brakes rear ends,transmissions)in there mopars because of them being more readily available and cheaper than the oem mopar stuff.I'm just curious if anyone is running Ford or Chevy motors in their A body mopars..being how there is a large supply of them at low cost compared to hipo mopar engines.Or is it possible that this is where the line is drawn in the sand and you get kicked out of the so called mopar club?