Paul,
I fully understand the limitations of Fractint's mostly very, very old code, so I certainly affirm the need for the improvements you suggest. I'm certainly not a candidate to help. I have been happy to provide web hosting for the project and occasional testing, and still (just barely) have the ability to recompile the old DOS code. I tell myself I still could jump in and code, but the truth is I haven't in decades and have been retired now for eight years from my NASA software development career. And I have a very full and satisfying life, of which fractals take just a tiny part. So I'm not a candidate to help you disentangle some legacy Fractint code in ManpWIN.
Good luck! I'm not saying you should do this, but if you made the ManpWIN code and development environment public, you never know who might appear. Over the years I have received many messages along the lines of "Where's the fractint code? Point me to it and I'll make huge contributions before next Friday". Of course, in every case, we never hear from them again, because the source code is daunting. But others come from out of the blue, and their first message to us is that they have made some amazing contribution already, and sent it to us. Having the code public makes that possible. Not saying you would have that experience today, fractals are not the big deal they were with Mandelbrot was writing.
Tim