Hey, welcome to NICO Club! I think you either use the old distributor with the old computer in this new engine or use the new distributor with the new computer and new engine. IF the yard who sold you the engine has sold you the wrong stuff or mislabeled it of their own fault, they may have the proper engine computer and they may just give it to you as apology for their mistake. If there is no such liability on their end, you may have to pay for it or seek out another one. I don't think there are too many differences between 84 and 86.5 as far as technology goes. What physical differences are you finding? Anyway, if it were me, I'd probably try my older distributor so I could use my older engine harness and computer.