Asking a bunch of custom builders their advice on what bicycle option is best will naturally need to our recommendation to get a custom frame. Trying to adapt some of your racing type of bicycles to fit your latest body is going to lead to a compromised result. You need to find a builder that can make a frame exactly to your new position. Frame design can broadly fall into 2 philosophies. The 1st and most common (and what you are probably most familiar with) is make it as efficient riding as possible and handle well. Unfortunately that works best with the young and fit. The 2nd method - and the one I'd recommend to you - is to get a fitting on some kind of fitting device and find out what position you are now most comfortable being in. The fitting bicycle should hold your preferred seat and handlebars and be able to adjust them until you are as comfortable as possible. The problem with trying to switch out bars and stems on one in your fleet is that your frames may still prevent the best possible position for you. Once your new position is established, the frame can be designed around that new position. What I think you are likely to find is that - if you are going to try and use drop bars - your handlebars will probably be well above your saddle height. That will rotate your seat position back requiring a 70/71º seat angle. It is also quite possible you may require "North Road" style of handlebars like what is used on English 3 speeds. Those will position you much more upright. Bicycles designed around those handlebars require very slack seat angles. My wife and I enjoy riding this kind of bicycle on MUT.

To summarize, 1, get a fitting while perhaps trying out a new saddle and handlebar shape to find where your remade body is most comfortable. 2, Have your framebuider design the frame to match your new found seat, handlebar, pedal position. 3. ride happily until you eventually die.



This style of bicycle is great for more casual upright position riding.

This is my Ukrainian made fixture I use to design a frame around a seat and handlebar position,