It will be really difficult to maintain the 1:1 scale without using FormboardXC. HarnessXC didn't have enough constrain to avoid an erroneous move/manipulation.
The best way to keep it possible will be to place the bundle as per a 3D bridge out harness (From and ecad like Catia, NX or ProE), but the aspect ratio will not be guaranteed, or, you may create an Harness from a Full-Scale Topology (Topology build with the same 3D bridge technique).
Also, I know it is available in FormboardXC, but I never test on an HarnessXC, but you have a DRC that will check if the visual Length meet the real length.
For the bundle size, you can create a plugin (API custom action) that will assign the graphical bundle line size with the same size than the bundle width.
finally, I don't know basic tool in harnessxc that will check if your bundle bend radius is respected when you add an arc (important to respect bend radius on a formboard in order to didn't create bundle bird cage, or overform a curve, but you will not have this issue if all your bundle are straight or only have very light curve)
John, can you expand on why you are trying to create a 1:1 diagram? Capital Formboard is the product that manages full-scale diagrams as well as providing functionality around Formboard specific tasks (e.g. fixture placement).
1:1 diagrams are required by our prototype harness supplier.
In that case you should be using Capital FormboardXC as it is explicitly developed for this purpose.