Is there a difference between the early 2nd gens and later second gens in regards to the heater box?

 

My moms truck is smoking out of the vents and is an early interior 2nd gen. Need to start gathering parts and was wondering what swaps between the them

44 minutes ago, Silverwolf2691 said:

Is there a difference between the early 2nd gens and later second gens in regards to the heater box?

Yes. The blend door is is mechanical in the early and the later is electronic stepper motor. Rest is all vacuum controlled.