I bought a 360 Magnum from a friend recently. He told me that it was a 2001 model factory crate short block. He had a machine shop finish assembly to the 380 hp crate motor spec's. After assembly it sat in a sealed container for 9 years. He told me that it was an LA balanced engine. I had a local shop install the engine in my car. It had a horrible vibration in it. It had one of those heavy weighted 360 vibration dampers on it, the one with the big offset blob of steel on front of it. I replaced it with a Mopar performance #P5007301 vibration damper. After that things got a lot better, but the vibration is still there just not as bad. The mechanic swears that he put an LA balanced B&M flex plate on it.
My question is; Did Chrysler build an LA balanced Magnum short block? How do you tell which balancer is required. Is a Magnum crank different from an LA, or is it the connecting rods, or both?

The '93-up magnums have a slightly different balance to them vs. the

LA engines prior. The vibration dampener and flex plate are

different.

the magnum uses less external balancing weight then a LA 360, the pistons and rods are lighter. ...as said above use different damper and flexplate then a LA 360.

I put a late model damper and flex plate on the 360 Magnum I put in my '72 Charger.

im no expert on magnums as i only have an early 360 crate.they do require a different balance than an la engine.i used a b&m flexplate for magnum 727 with a 0 balance converter and all is well.you also need to check the balancer as it will need to be matched to the crate 360

I guess I need to pull the oil pan and look at the rods. Does anyone know the visual difference between magnum and LA rods?

the rods are narrower on the small end where the pin goes thru...the magnums are less then an inch in width.

Looking at the rods isn't gonna tell you anything, instead look for any stamping on the crank that might be the record of a balance job. Otherwise I would just assume it's a stock Magnum and external balance accordingly.