289 Timing issue

Going to start out with some basic stuff since I didn't see it covered above . . . .

Are you sure all wires were placed on the correct plug locations as before? If they are mixed up the motor either won't run or won't fire all the cylinders it the proper time. Also note that the plug wires are placed on the cap CCW as the rotor spins that way when the motor is running.

Being a 4 cycle motor the crank rotates twice to every single firing cycle needed. Are you sure that you were at the top of the compression stroke when you inserted the distributor? If not, pull #1 spark plug (secure the plug wire away from your body) and place your thumb over the hole where the spark plug came out of. Have someone "tap" the starter until you feel pressure wanting to blow your thumb off the hole. This identifies the compression stroke. Then manually rotate the crankshaft CW by hand until the crank shows TDC. You shouldn't have turn it in that direction more than 1/2 a turn. Then align the rotor to #1 spark plug.

Have you timed this motor in the past? There is always the off chance that someone might have changed out the timing cover and the timing mark on the cover was relocated to a new location. Normally a 289's pointer is on the driver's side at about the 2 o'clock position.

The installation of the intake gaskets could be suspect and that would lead to a vacuum leak which would interrupt the proper fuel/air flow.

Have you ran a compression or leakdown test on all the cylinders? Perhaps there is a problem with the head gasket installation (although probably not likely if your thumb gets blown away from all the cylinders as mentioned above.)

And last but not least, do you know if the camshaft has been changed out before? Some SBF cams have cams built for a different firing order but will work fine when the correct firing order is used. The 289 firing order is 1-5-4-2-6-3-7-8 and the alternate firing order is based on the one used in a 351w. That one is 1-3-7-2-6-5-4-8. The wire locations MUST match the cam but luckily there are only the 2 different firing orders to try. The wrong one will make the motor run half azzed since only 4 cylinders will fire at the correct time.