this is a much harder question than I would have thought , The factory service manual tells you to check the emissions label in the engine compartment, I am guessing you no longer have one. Haynes is only giving the timing up to 79 in a book that is supposed to be good up to 89. For what it is worth the timing on a 79 AMC 258 i6 / 4.2l two barrel with manual Transmission is 6-8 degrees BTDC and the auto is 8-10 BTDC. I am pretty sure I am running my 81 J-10 AMC 258 i6 / 4.2l manual two barrel at about 8degrees BTDC.
Thanks guys, you wouldnt believe how far off it was, cant believe it was running. Exlpains the loss of power. I still have a wobble at 35-45mph under load, it goes away when coasting. It feels like a miss and doesnt appear to be in the drivetrain. Basically developed this overnight?