You might see if a local LBS will let you try a 70mm 7 or 17 deg stem, maybe flipped. As long as there isn't any damage, they have nothing to lose, and neither do you. Doesn't hurt to try.

Your cockpit mis-fit echos the problems I had with 2 bikes, so One is fixed the other is yet to be tested. I'm not the same as I was when I received my '75 Sekine (in '75). I felt streched a bit. So pulled the front curve of the bars back by a full 50 mm by getting different bars and went to a 60-ish mm quill stem. Then I actually lowered the bars another 10 mm and walla! The frame is too long for my comfort, so the drastic short bar/stem combo actually gave me better control.

Next is my newer bike a 25 mm shorter effective length in the top tube, threadless stem, but the 105 brifter hoods are longer than on my Sekine. I switched out the 100 mm 7 deg stem for a 75 mm 7 deg flipped stem but haven't had a chance to test it yet. I wanted a 17 deg flipped stem just so I get lower without removing lots more spacers. Aesthetics, I know.

Down and back can be a good thing. You will here folks say a short stem is twitchier, but most reading I've done says you get used to it pretty quick, and actually I had better control because of less stretch - probably because of low core strength.