Originally Posted by
Lascauxcaveman
My extra tall and long Nitto stem worked "OK" on getting my 56cm Trek 2100 rideable for me, but ultimately, I sold the bike. All my bigger bikes just felt better, even thought they were all at least 5lbs heavier...
Pretty much this was my experience with my same-sized 1984 720, except that I was a little shorter than the OP, and the bike still felt too small.
The inexpensive stem quill adapter would allow the OP to verify whether a taller bar really makes the bike comfortable, but the bars on these bikes have a narrow stem clamp diameter of about 25.4mm, so an older MTB threadless stem would fit best on the adaptor.