I have the opportunity to buy a (used) rs dx300 or a -302.

Never owned a 300 but have a 302 (someplace, haven't seen it since I moved)
that I used with an AEA CP-1 to copy cw and rtty. It drifted a dab when it
was first turned on but stabilized after 10 - 15 minutes. The 302 (not sure
about the 300) was made by GRE, the same folks who produced RS's Pro 2004, 5
and 6's. My only gripe was the outer tuning ring (the one that dialed in the
MHZ) was very stiff and hard to turn and didn't agree with my arthritic
hands. Don't know if that's normal for the beast or was just a problem with
mine. Not a bad radio if it can be purchased right (75.00 absolute top for a
nice clean one) but don't hock the farm to buy it. RM~

PS, It is very old and a lot of critical parts are no longer available.