1999 Dodge Truck ok to swap a 360 efi down to a 318?

I can give you some suggestions based on older engines. The 360 was an externally balanced engine meaning some of the crankshaft counter weights aren't on it; they are on the harmonic balancer and flywheel or torque converter. To prevent vibration, you have to keep the torque converter with the engine.

The flex plate could change from year to year but they could interchange. Look for one offset mounting hole where it bolts to the torque converter. If that matches, look at the notches cut out in the outer ring. They must be in the same exact location and have the same number of notches in each group. These tell the Engine Computer when to fire which cylinder's spark and injector.

You could run into problems with the Engine Computer and wiring. It is programmed to fire each injector for a specific number of milliseconds. It can adjust plus or minus about 10 percent for emissions. You should try to use the Engine Computer from the 318, but the rest of the wiring harness could have some differences.

Caradiodoc