There were 3 main harmonic balancer designs used on the 3800

The L67 balancer has 2 sets of belt ribs on it since the supercharger was driven by its own dedicated belt. This extra belt required a longer balancer to allow for it.

The naturally-aspirated engines were only equipped with one set of belt ribs on the balancer because there was no supercharger to drive for these engines.

There were 2 different balancers used on the L36 engines. This is because rear-wheel drive vehicles came with a slightly different balancer than the front wheel drive vehicles.