Find a local motorcycle shop that supports race bikes and ask them who makes custom jackets. The jacket will have to fit tightly so that it won't move while you're wearing it. They can make a jacket that will make it safe to wear a 4/5 harness. As to cost, I rate it like a helmet, what's you brain worth. In your case what is it worth to race your car and not have to worry about popping an artery or ripping a graft. As a side benefit, once you've had the jacket made for a pretty penny you'll have a great reason to stay in shape and avoid gaining any weight
When you find a leather jacket maker they should be able to hook you up, not cheap, but better then internal bleeding. Picture a jacket with a roll of padding on each side of the area to be protected. On top of the rolls is hard shell cover creating a cavity over the artery and graft. It can be made so that it follows the belt, that way the pressure would be evenly distributed. Once it's made you could show it to your Dr. and tell them who made it. That way if some else is "nuts" they can send them to the right people. Heck, if you get the right tailor they could make a full chest protector and put the zipper on the side. Years ago I saw some really creative padding on leather racing jackets for a guy who had nerve damage, so I know it can be done.
Just search until you find the right guy and don't spare the pennies. We kind of like keeping members around and we'd hate to loose somebody for the sake of pennies. Matter of fact we might just get a little cranky.
- Joe