If you've been riding with a drop bar since 1968, the shift to an upright posture is going to be a bit of a shock. I tried it and failed, and I've only been riding drop bars since 1978!

Try this. Assuming you can ride no hands for a little while (or with the bike set up on a stationary trainer) take your hands off the grips and hold them just over the grips. Your abdominal muscles will have to take up the slack. Now straighten your back a little and watch where your hands go. Depending on how straight you want your back, your handlebar grips are going to have to come up and back.

I wouldn't worry about the seat. You've been riding long enough to know where you want the seat relative to the pedals; it's the hand placement that's unfamiliar to you. Once you get that* you'll know if the seat has to move as well.

*but like I said, I couldn't make this switch. My upright/flat bar bikes are set up almost the same as my drop bar bikes, and my posture is never very upright.