Sew grass without tilling?
I recently bought a house whose lawn was originally done in 1951. An area measuring 115' by 36' was allowed to be overcome by pachysandra, which I have removed. I'm comfortable with the process of sewing grass in this area, but I expect the new and improved cultivars of KBG, Perrenial Rye, and Chewings Fescue are not going to match the old Common KBG. This is in a prominent part of the front lawn, and I'm expecting a noticeable line between them.
So I'm thinking that later this year, I'll need to kill the remainder of the old KBG and sew the same seed there. But I've heard that some folks simply kill the grass, fertilize, then sew the seed over the dead grass (which acts as a mulch), and don't bother tilling. I'm curious if anyone here has had experience with this, or has an opinion. The remainder of the front lawn is over half an acre, and it'd be nice to avoid roto-tilling, if it's not really necessary.
I'm in Pennsylvania, in an area with fairly organic soil. The existing lawn doesn't have significant thatch or soil compaction.
Thanks for any advice.