The fuel mapping parameters would also be different (as Michael pointed out about 8 injectors versus 6).
The original Pentium chip has the same number of pins as the Pentium 4, but I'll bet you couldn't just swap out your old for the new without some major software (and hardware) changes!!
Buy the chip and sell it for a profit at the next MB swap meet!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car