If you want to match your position on the new bike, you must start with setting the saddle at the same height and setback from the bottom bracket. Measure the distance from the saddle tip(assuming you are using the same saddle on both bikes) to the handlebars on the old bike. Also measure the drop from the top of the saddle to the handlebars. Use whatever length stem and spacers necessary to put the handlebars in the same place, relative to the saddle, on the new bike. That will match your position/body angles from the old bike to the new. The ride characteristics may not be the same, but your body will be in the same position.

This is not really a framebuilding question and you may be better served in the Fitting Your Bike forum.