I've got a Poulan Pro PP4620AVL (no need to laugh, I'm poor and it was inexpensive) with a 20" bar that Oregon's website says uses a .325 pitch, .050 gauge, and 78 DL chain. Everything else I've read confirms this. In the future I'd like to go to a 16" bar, I'm guessing I need .325 pitch, .050 gauge with 66 DL chain. Is that the correct number of drive links? I'm confused since the 20" chains of the same pitch come with 72 and 78 drive links. If the pitch is the same it seems like the two different number of drive links would change the length of the chain.