ROTICKA

I have a 1984 Trans Am. It had a carbed 305 H.O. originally. I bought the car a year or so ago, from a guy who had swapped in a 350 T.P.I.. 1988 I was told. He replaced the computer, and fuel pump, those are the only things I'm sure of. Since I've had the car it has been a real fight to get it running right. Things I've replaced: Fuel pump relay, MAF, CTS, Oil pressure guage, TPS, Coil, Distributor, Cap, Rotor, Plugs, Wires, Thermostat. The problem I'm currently trying to fix is no timing advance. I set it to 8 degrees btdc with the est wire unplugged (the timing mark jumps around by 2-3 degrees, only holds steady when car is in high idle) plug est wire back in and no change. No advance, no retard. The only thing left to replace would be the ESC module. My question is - Does anyone know how to tell the difference between a 305 and 350 module? The number on the module I have is HKM 882401 (Niehoff). The cheapest one I can find here in Missoula Montana is $85.00. I would hate to throw that money away if it is not the problem. Any experienced advice would be appreciated. Thank you, Sonny.