Here's the reply I gave for a question in the Sportster forum. I also just use HD filters for both.
Engine oil's separate in Sporty and Twin Cam engines. I use Mobil 1 15w50 in both bikes year round. $25 for 5 qt. jug at WalMart. Can barely get dino oil for that price anywhere else. I've tried several different oils and the Mobil 1 is as good as any.
Here's the stuff for Sportster trannys and the primary on TC's. Redline Lightweight Shockproof. Redline recommends it for Sportsters so I tried it in the Dyna primary too. Clutch plates separate when clutch is disengaged, so hold the clutch in for a second and usually no more clunk into first gear on the Sporty, and never a clunk into first on the Dyna. Fantastic stuff......
Redline Heavyweight Shockproof in the Dyna Transmission too.