Gary, at first reading I mistakenly thought you had replaced the coil/power pack. Now thinking otherwise, I suggest the following based upon my own 740 Rex experience.

Cleaning the up the Rex/Regina coil pack fixed a no-start problem I had. Whether it was due to dirty internal contacts or oxydation on the mating surfaces I really don't know. All I know is that I cleaned everything and then the car ran fine. I do have to say that the internal contacts had what appeared like some hardened crud on them kinda like 100 year old dielectric grease. Unplug the high tension lead and the other harness connection. The pack separates by removing a couple of fragile Torx screws that secure the coil in place. Once apart, you'll see the (three I believe) internal "springy" contacts. Scrape any accumulated crud off of the cantacts and the pins that mate to them. I've even bent the springy contacts a bit to assure good contact with the pins when re-assembled. Also clean up the mating surfaces of the two halves of the pack to assure good grounding. There is some argument as to the importance of cleaning up the pack-to-chassis interface, but I do it just to be a good boy, besides, you're there anyway. A light coating of dielectric grease on any mating surfaces isn't a bad idea.