870 isx replacing a 871isx.

[herschel]

i have replaced a blown 2009 isx871 in a pete for a 2003 870 isx out of a volvo. everything bolts up great now how do i deal with the computer? with the wiring harness in the pete hooked up the engine will start and idle. i changed the tps to a 2003 pete that would have a 870 isx. as the two engines are completely different do i need to replace the harness from the engine to the cab? would the 871 computer be a better choice on the 870 if that can even be done?i do have a guy coming to plug into the computer but was hoping to have most of the preliminary work done. were do i start? i have the harness out of the volvo that plugs into the 870 computer and goes to the fire wall. kind of a head scratcher for us old guys but cant be that tough to straighten out. the 50 pin plug for the volvo uses about 11 pins, the pete uses about 30.thanks in advance for any and every bit of help.