Center Board Repair - in my experience the rust-converter chemicals don't seem to do much beyond a very thin surface layer. That means your success will depend on how well you can sand (first) and wirebrush (second) that rebar. Also, there are two types of the rust converter. One is almost pure acid (diluted to the proper strength) and you can tell it by the fact that it is clear. The other is mixed with some gunk that purports to turn the rust into a primed surface. You can tell it by the fact that it usually is milky.
The former, if you rinse well, will not add any layers to the surface, so with a light wire brushing you should be able to epoxy to something like bare metal. The latter can be insidious in that it can form what looks like a nice "primed" surface, but if you had too much rust in some spots, that surface could sit on the outside of the rust, and there's no way, short of sanding off the "primed" layer to find out what you have.
If you mix your epoxy well and in correct proportions and clean the surface well (soapy water) and sand it, you should be able to still get that high strength filler that I mentioned to bond to it, even though it's polyester based.
Here's an extremely schematic drawing on how you could use filler to improve on the factory foil shape of your CB.
You can make the leading edge very round and try to build up the "ramp" on the leading edge side (top and bottom, not just top as in the drawing). Because I wouldn't suggest sanding into the existing glass cover, it's not possible to make as long a trailing edge as the ideal foil shape would require with this method. However, you can measure your trunk and CB and usually there's room to add .5" to .75" to the trailing edge, allowing you to draw this out to a fine point (and sand off to 1/8" or so). My technique for doing that is to fold a strip of wax paper (or stiff plastic foil) and use that around the filler so you can "massage" it into a rough shape. Once cured, you sand the final shape.
Other people place the CB w/ trailing edge down and laminate some fiberglass cloth on either side that they let hang down. They let the cloth connect at the new location of the trailing edge, which creates a hollow space. They fill that space with thickened epoxy. That technique is fine if you already need to put new glass down (like over a new wood cored CB). If you don't, I like my technique. It gets the job done in a single pass (with some sanding).
Even if you can't get the best theoretical foil shape, getting your CB as smooth / fair as possible and fairly polished will make it behave much better. This almost certainly entails several coats of fairing compound with sanding in between.
Transom - that's good news.