K3STX: "I thought I read somewhere that some 6C4s were better than other 6C4s for the drift"
There may be a slight difference; it depends on the situation. No harm in trying all of the 6C4s you've got; if nothing else, it will tell you if any of them are bad.
But there's no point in buying more in the hope that one of them will magically eliminate the drift, because in a receiver like the '170 it's due to a whole bunch of things.
K3STX: "since I am using a DX-20 as my TX I am not scouring the bands looking for weak signals anyway."
Why not? You'd be surprised what can be worked with a decent antenna when conditions are good.
Since the first of the year I've been spending a lot of time down on the low end of 80 CW, in the evenings. Without really trying I've snagged MD0, GI0, UR8, E77, ZS1, and a couple others I can't recall offhand. The rig I used is the one shown on QRZ.com; the antenna is a homebrew inverted V with traps for 40 meters. Center at about 40 feet, ends maybe 12-15 feet, on a small suburban lot. Of course some of those DX stations have pretty big setups, but they all came back to me and gave good reports.
Your DX-20 is only about 5 dB down from my 100 watter.
73 de Jim, N2EY