flat tappet cam 302 in a 302 roller car

1987 Ford LTD with a roller cam 302. I installed a rebuilt 302 from an '85 flat tappet Merc Grand Marquis into a '87 Ford LTD equipped with a 302 roller engine. The computer is not at all happy with the cam change. I have to run 20 degrees idle advance in order to get reasonable smoothness at idle. Is it possible to reprogram the computer to accept the older engine. Could a computer from an '85 model be installed in the '87? Would the early computer fit the '87 wiring harness?

Thanks for your help