Your height in cm is impossible as written. Your inseam in cm is about 31". Mine is around 33". I am 5'10". I should probably ride a 58cm frame. I found a 62cm old style horizontal top tube frame. In shoes I can just about stand over it. That's called "French Fit" by the Competitive Cyclist website. I use the stem it came with, 110mm and it fits (fingertips reach the handlebar with elbow at saddle nose) because the top tube is around 57.5cm. On another bike with a sloping top tube I was able to make an XL frame fit, by using a 90mm stem. Maybe a longer stem would make it less nervous and maybe not. Its a tandem. Tandems feel weird no matter what you do. I suspect you will be able to ride the big frame. Why not plug all your information into the Competitive Cyclist Fit Calculator. If your frame is bigger than what CC calls "French Fit" then you might have problems with it.

H