Question

Please help me.I have had my 86 firebird to 2 different shops each had it for a week with no luck fixing it. I cannot afford to keep taking it in and paying for it NOT to be fixed.
When setting the timing w/ distributor unplugged, and then plugging it back in the car will barely run. Setting the timing with the distributor plugged in results in the car running but with little power. I have replaced the modulator 3 times, the pickup coil, coil, cap, rotor, wires, plugs, computer and the catalytic conv. back to the tailpipes ( cat was shot and exhaust plugged ).
Is there a chance it has the wrong computer in it ? The reason for asking this is that a friend has a 86 camaro with a vacuum adv. distributor, mine is an 86 firebird with no vacuum advance and we have the same computer. ( it seems to me they would be different ). My research shows 2 computers for these cars, XXXXXXX which is what we both have, and XXXXXXX. It is a "H" code 305 carbureted. I bought the car running like this. The timing is 70 degrees off to be able to drive the car. PLEASE, PLEASE HELP !