Well, as for the prop disc, I would just take one from another plane, rename it and substitute it. I don't recall any need to do that, but it's been a long time since I did the conversion.
For the CG and such, I've attached the two sets of flight files I got here several years who when I first did the conversion. One set is a modification of John Young's AI flight model made by Norm, who shared them with me when he taught me about this process several years ago. The other one is by another denizen of SOH who adapted them from a different, B-25, a flyable one, but which one is unknown.
I should have thought to attach these files and the 3D model to my initial reply to your inquiry, but I didn't think of it then.
I've used this little trick on a number of non-VC models. It usually works out pretty well. I've converted a few non-VC flyable planes, like models by Mike Stone and Kazunori Ito before he started making VCs. I was very surprised to find that one of Mike Stone's airliners (I forget which one) had a complete flight deck with all crew stations that coldn't be seen through the little cockpit windows, but from the inside, with the 3D model made visible, there it was was.