jayinpalmharbor

i bought an FD rx7 that had a gm 5.3l in it. I was told i could use the LS1 harness and had it all wired up. my mechanic is now telling me the ecu will not work and i need to get another. something about the pins not matching up. is this correct or is there an easier way to fix it? if i was to get a different ecu what do i need to get? is there vin protection that will keep me from using it? thanks!